As neat as the Bootstrap grid is, the day that we have broad browser support for the CSS Grid spec cannot come soon enough.
Even enough support to use flexbox on a daily basis would be great
I think we're rapidly there: core support is around 80% or so now, which is definitely in the range where using a polyfill for the remaining IE 9- users is plausible for many sites.
It'll be nice when you can assume full support but I'll take vertical centering, easily consistent heights across elements, etc. now.