Unfortunately I have to agree with this precisely for the reasons outlined by Casey in the parent's linked video. The shift from standardized ABIs to driver-abstracted hardware has ballooned the code required to work on "a PC" geometrically. It's basically impossible to catch up to established OSs now.

An alternative would be targeting a single set of hardware that's likely to be around a really long time. I'd be ok with that and something like a Raspberry Pi, but only if all the hardware was open. Of course, then you're in more of a 68k Mac space where hardware choices are extremely limited.

Mainstream OSs are good at what they do.

I think we are talking about a different niche.

If so, no need to think in terms of catch-up. Rather: work out the design values of this niche.

Lots of ideas, but this thread is already deep. I have created #dinghy on irc.freenode.org, would be interested to discuss further.