It was TS's 2.0+ idea to stick to Stage 3 like glue. Especially prior to 1.0, but even during 1.x, TS implemented proposals in stages earlier to 3 (or even not yet staged). One of the regrets you sometimes hear from TS devs is that they added decorators way too early (it's still not Stage 3 and increasingly likely if it ever hits Stage 3 it will look very different, and it may never hit Stage 3 because there is a bunch of opposition), even though that is behind an "experimental" flag, there's a huge amount of "Production" code written with decorators in Typescript. (Largely thanks to the Angular ecosystem that became hugely dependent on decorators.)