This would help with stuff like 3D libraries and generally improve the performance of Snap! and a portion of projects that are very laggy already.
Sounds good! However, I suggest it should be gone for users with no WebGL or an Old WebGL, like when unregistered or new Scratchers have cloud variables option hidden. Support.
that's not WebGL is.
anyways it will fallback to canvas if no WebGL
Just switching to webgl is not as simple as that. Since it is a completely different rendering engine with a different api, which would take a lot of time tp switch over tp using (ok, I did find a library that reimplements the context2d api into webgl, which snap could use/ but it still would need a bit more work to use).
Snap has way better things to worry about than the render engine, especially since in most cases, snap runs smoothly. I cannot speak for Jens, so he can very well have a different take on this.