Gatekeeper was added in 2012, and required the user to either take steps (right click open, or disable gatekeeper via the Gui or command-line) to run apps not signed by a developer ID, which costs $99/yr.
Eventually Apple removed the option to disable Gatekeeper via the GUI due to developer abuse (e.g. games, including Minecraft, walking children through globally disabling security settings rather than signing their apps).
Notarization doesn't add the requirement of signing, nor does it change that you need a developer ID for $99/yr
The change is that in each release of Mac OS this process is getting harder to avoid and is starting to include additional requirements. "You need to sign apps" becomes "we need to run an automated review on our servers for every release you make." This matters because a lot of the original criticism around the original Gatekeeper was dismissed via the argument that it was just an optional security feature that was turned on by default. It wasn't like Apple was going to block 3rd-party marketplaces, this just made Mac OS safer for computer illiterate users.
With El Capitan, people are starting to suspect Apple does not want unvetted apps on the Mac in any context, and it seems more likely that future Mac OS versions will continue the trend of having stricter, more burdensome vetting requirements.
It is increasingly harder to take advocates at face value when they say that 5 years from now I'll be able to run a 3rd-party app on my Mac that didn't go through a manual review. Which might sound great to some people, some users love the app store.
As to why I think that could be a problem for creative mediums, see my parent post. It may not matter if Gatekeeper begins to live up to its name, because creative mediums may just migrate off of Mac. But if Mac becomes a platform too big to ignore, or if other platforms like Windows follow suite, then I think creative mediums will suffer.
This is about whether a 3rd-party application downloaded from a 3rd-pary website can be run. It used to be that you only needed to pay to get onto the distribution and advertising channel, now you need to pay not to make your user jump through special hoops on an admin account.
It's not implausible to suggest that in the future, that loophole will be removed as well. Apple does not want you to download apps that they can't personally vet.
The complaint isn't that you need to pay to get into their store. Of course you do, that isn't surprising to anyone. It's about whether distribution channels exist outside of their store.
As to why that's a problem? To quote the author:
> It really upsets me because the iOS App Store policies basically prohibited art or anything interesting (nudity, glitch, error art...temperamental depending on who reviewed you for approval).
> It was hell for me to get things approved, and even when I got them approved I had to change so much about my work it really wasn't my work anymore. A platform holder shouldn't dictate so much about someone else's work.
Apple has been consistently behind the curve when it comes to recognizing the artistic potential of games[0]. On a cultural level, we don't want want them to be a gatekeeper for a medium. As a company they aren't responsible enough or smart enough for that job.
[0]: https://www.theverge.com/2013/1/16/3879194/apple-app-store-g...