I think the main issue isn't that it is heavy to transfer, but bootstrap is a lot of code to wrap your head around, if you want to customise beyond the defaults

I think the main issue isn't that it is heavy to transfer, but bootstrap is a lot of code to wrap your head around, if you want to customise beyond the defaults. I think a more lightweight core could be worthwhile, although I'd rather see Bootstrap slimming down, since it's otherwise a very good framework.