dtplyr, the dplyr backend for data table is still IMHO not great, and will often break in subtle and not so subtle ways. Tidytable is, I think, a much more interesting implementation, and gets close to the same speeds.
Hmm, this looks very interesting! I've ended up preferring dplyr for it's expressiveness in spite of the speed difference, so this might be a nice compromise for when dplyr gets too slow.