Mono Relicensed MIT

Wow, really? Can you provide a link? All I could find yesterday were some articles that claimed sime restrictions imposed by the app store would somehow be a problem, but nothing as concrete.

At least that should put all questions at rest which side is at fault, such an explicit rule makes it clear that it is the app store.

> A user will be able to get a GPL-ed source but won't be able to distribute it or even use it, except by paying Apple and putting their own devices in developer mode.

I am afraid I don't understand where you are seeing any problem there.
Anyone with access to a GPL-ed source can distribute it, e.g. putting it on a digital media and given that to someone, or uploading it to a server.

For using source you need to either be a developer or have easy enough to follow instructions, but that is a property of source code, not of the source code's license.

Also not entirely sure what you mean with the last part but my guess is you are referring that deploying a modified version onto an iOS device would require Apple's development tools and a device that allows out-of-store installation.
In that case I also don't see how using e.g. a BSD licensed source would not also require that. Again a property of having access to a programs source, independent of the source's license.