If there were performance costs this can be mitigated very easily - to be able to do compile time checks means TS is designed largely around early binding, at least in the default case. A JS engine can do this trivially.
> > related page load perf impact > Type annotations would likely still be stripped by minifiers, just like comments. No change.
You're kidding right? You're proposing permanently changing the language, in a way that burns the type syntax for a feature that you're now saying will be stripped before a JS engine ever sees it?
> As a dev that regularly uses TypeScript, being able to use debug builds with annotations and copy paste TypeScript into the console would save a lot of time.
That sounds like a feature for your console, not the language
> This would be part of larger trend of adding type annotations to dynamic languages. Python, Ruby, and other dynamic languages have blazed the trail here.
Which enforced the types. Understand I am not opposed to the type annotations, I am opposed to this because it does not enforce those types. That means that broken content will exist, and thus burn the syntax.
> There are ways to add enforcement in the future if needed, just look at 'use strict';
Which will never happen again. As the person who implemented strict mode in JSC I can tell you that the cost of a mode switch is massive, in spec and implementation complexity. Adding another mode switch is simply not going to happen. The only reason I was ever ok with adding strict mode to javascript was the removal of the this conversion. No other part of strict mode would have warranted the cost.