Would it be feasible to mark extensions as JS only, like with an icon next to the name?
It could confuse new people why new blocks aren’t showing up.
Maybe an icon that looks like this?
EDIT: After messing around a bit in Paint, came up with this:
Yes, it’s very pixelated but if you made it at a bigger scale you wouldn’t see it. 
Nice. Really funny in a way
This is actually interesting but i don’t use JavaScript 
That is the only reason why I dont tweak javascript games i dont know how! 
Definitely feasible, and a great suggestion! I’ve filed this in Github, where we do all of our issue tracking: https://github.com/microsoft/pxt-arcade/issues/2391
We love when users report bugs and propose features! You are also welcome to submit your own issues for Arcade here: https://github.com/microsoft/pxt-arcade/issues/new/choose After the issue is filed, we will label it and begin fixing as we work towards our next release (we just released Arcade, so it will probably be a little while until the next one).