If I recall correctly this case even went to court.
Now remains the "suck the brains out" problem, and although it could have been easily solved cooperatively IMO, it is illustrative of why people would not have needed 3rd party DOS when Windows 9x was running anyway: the kernel did nothing, the libs were mostly irrelevant (and MS-DOS probably gave that small compat edge even there, simply because its prevalence even before 9x), and the cmd line tools, well a) who cares about the tools b) actually if you do I suppose that was the easiest things to run (and if not: the irony; oh it is scandalous that windows relies on internals of MSDOS -- but not that e.g. Caldera DOS tools relies on internals of their DOS kernel)?
Caldera would have needed a Windows clone to compete. DOS was just becoming irrelevant.
* It becomes much easier to make legal noise about Microsoft pricing. If they're saying "Buy Windows 4.0 and we'll give you MS-DOS 7.0 free, or for some token sum" it's pretty obviously market dumping. If you had to pay, hypothetically $50 for MS-DOS 7 and $50 for "Windows 4", instead of a single $100 package, Caldera can compete with a $30 DR-DOS product even without having a Windows clone.
* There could still be a territory war over the quality of the underlying DOS. This was still a time when you'd have a lot of games, in particular, that required a drop down to DOS mode.
* There was also the opportunity to sell features that still had DOS components involved more modularly. I'm thinking about FAT32 in particular, because I can recall radio advertisements boasting about it to try to sell Win95 users on upgrading to 98 or 98SE. What if you could pay $10 and get a DR-DOS competitive upgrade that supported it instead of a full $100 upgrade with a bunch of features you didn't care about?
In such an environment, there could have still been 5 or so years of DR-DOS as a viable commercial product until the much less unbundlable NT-based Windows went mainstream. That's a significant amount of runway. Their pivot from there is not obvious-- I can imagine some attempt at a Linux distribution with a tightly integrated WINE setup, but that might have been too much to ask for at the time.
I also wonder how a Microsoft that had been clearly slapped and told "you must play well with others" in 1995 or so would have behaved over the next 20 years. The trajectory of IE would have likely been very different, and I wonder if they would have handled some of the other Office competitors with kid gloves to avoid legal scrutiny. Maybe even some healing of the rift with IBM on OS/2, so they could point and say "look, we're interoperable, here's another compatible product."
Well, Digital Research had GEM[0] since mid-80's. Development was probably halted after Novell or even Caldera acquisitions.
[0]: https://en.wikipedia.org/wiki/GEM_(desktop_environment)
The comments in his blog disappear every time Microsoft shuffles it around, so these discussions are lost forever.
LFN support did work in windowed command prompts, as there the vxd's were present and provided the extra int21 support. I rather doubt that changed through any of the later versions, as there was no engineering need.
Schulman's book described this in great detail.
The LBA format drives, and using different partition types would be entirely handled in the disk driver level, hence trivial.
FAT32 was a smaller and simpler change, as it would largely be driver level, larger FAT entries, and then treating the root directory as if it was any other directory (hence growable), rather than "special" (fixed) as in prior versions of DOS.
If Microsoft had been “nicer” they could have made it easier for DR to use their DOS to load a GUI that mostly acted as its own OS and bypassed DOS once loaded, but what happens once they get to XP?
(Of course DR / Novell kinda knew this hence stuff like Star Trek, but whatever DR’s vision of the future was never came).
Also total coincidence how the same strategy played out with their web browser a couple years later http://toastytech.com/evil/fof.html :)
And well even in the Windows 3 era DOS was merely used as a bootloader on modern machines. Of course Windows 9x took the concept even further. The contextual difference was simply that there was tons of DOS programs and games even when 3.x was out (esp. games) and that even if that continued a little bit for games, it quickly migrated as Windows 9x became a comprehensive platform with the needed APIs (plus more and more people having it). And the default boot UX that was kept as-is by most people.
So from a market perspective, 3rd party DOS + Windows 9x would probably have died well for 98 anyway, and probably become ultra-niche way before (well, was probably niche already just before the 95 launch...)
Not to say MS did not have anti-competitive behaviors during that era (or attempts e.g. the AARD incident), and of course even just strategies to compete. They are actually well-documented thanks to various trials. But there is also the usual taking of random tech dependencies for granted until the main vendor suddenly changes its stack: and OMG you can't run booted from another DOS. Hell even when parts of the tech stacks were actually documented, licensed and supported, sometimes it stopped to be the case on the next iteration: and then you can't use a Cyrix processor on a MB with an Intel chipset anymore. It is not necessarily an abuse of dominant position all the times.
And here the point of the original post was to say there could have been a Win9x capable DR-DOS, so I don't even see why you are talking about "the next major version of Windows wasn't able to be "integrated" with any non-Microsoft DOS" when it clearly could: simply the compatible 3rd party DOS capable of that was not commercialized. Should MS have been forced of cooperating with other companies to have parts of their OS interchangeable? I'm not sure. Apple surely did not have to e.g. thoroughly document and then advertise their PowerPC nanokernel as reimplementable by 3rd parties (not an exact equivalent, but it is impossible to come with exactly the same scope given the two systems are so different, so I'm just taking a random component that can be distinguished from well-known and previously existing one) -- but then if some found an interest in doing that without support, they also could have done so.
Even if Windows 98 would be installed on the machine, running the software on plain MS-DOS would be drastically faster on those days when having less services/GUI on the background.
They would access the extended memory using the HIMEM.SYS driver and the run the software as bare-metal as possible. Not very different from what happens with linux servers nowadays.
This is a half-truth, due to the word "artificially" -- it implies nefarious intent by Microsoft to not let you run Windows 9x on just any old DOS. Microsoft determined with Windows 95 that Windows would be their primary operating system, and while it was still architecturally similar to the older 1.x-3.x versions that would install and run on top of MS-DOS (including various versions of which), that both components would be improved by developing them together. The original Windows 95's version of MS-DOS ("7.0") added support for logical block addressing and long file names in FAT. The second one in 95B ("MS-DOS 7.1") added support for FAT32. The Windows Me version ("MS-DOS 8.0")... well ok I don't really know of any practical changes aside from no longer parsing config.sys/autoexec.bat.
Still there were obvious compatibility and practical advantages to developing them in tandem. Massive improvements in the file system were feasible in the era that 2GB and larger disks started appearing on the market, simplified boot process as it was assumed that Windows would always be expected, some data structures could be rearranged or axed in order to allow Windows itself to manage resources.