Flex, HairWorks, VXGI are all no go unless someone comes up with some way to port stuff easily from old custom rendering to new one. Epic hasn’t even made any guide for but I do know the places where to look for in engine code. FleX additionally requires all physics changes fixed from 4.21 (which was main reason why there were no 4.21 FleX) so FleX isn’t happening at all unless Nvidia or some other community member does it.
At point, ball is at Nvidia. If they publish 4.22 versions for any of these techs I’ll happily merge them and possibly upgrade to upcoming ue4 versions but manually upgrading each GW techs rendering side (which is something I have very little experience with to begin with) isn’t happening from my end. 