It's good to see even experimental support for lessening the reliance on NgModules (which get in the way of appropriate tree-shaking), but I wish it weren't by doubling down on Angular's usage of non-standard Decorators. Requiring an experimental build flag in Typescript to even use Angular at all still feels like a red flag if not just outright poor taste in the framework architecture.
Yeah, that has always weirded me out, too, but I have assumed that because Angular is one of TypeScript's largest and most significant customers, that the flag is highly unlikely to actually be removed.
My understanding is that Babel already removed support for similar decorators to the ones Angular uses because that first attempt at TC39 decorators proposal was entirely revised and replaced with a very different decorators proposal. The "Decorators 2: Electric Boogaloo" proposal has actually made it to Stage 3 in TC39's proposal process this time which means that Typescript is going to be under pressure to add "real" decorators and remove the "fake" decorators that Angular currently relies on. I don't know how hard it would be for Typescript to support both medium/long-term but the transpilation backends for the two proposals are rather different to my understanding. (The new proposal is simpler, at least.)
Angular can certainly migrate to "real" decorators any day now, but my criticism stands that they could have already switched to the desugared form of the new proposal already (which resembles the desugared form of Python annotations) and have been better prepared for a migration. I've got a feeling part of the reason they haven't prepared for such a migration already is that maybe the DI is using too much Typescript-specific support in the "fake" decorators that maybe isn't likely to get carried forward into the "real" decorators.
I do think TypeScript's goal to be faithful to / eventually consistent with upstream ECMAScript would outweigh maintaining the current decorators for Angular.
So perhaps the most likely outcome is that TypeScript will at some point announce the deprecation of the current decorators, and this will cause Angular to have to migrate as you suggest.
