An improved Videl in FPGA has been done already - see the SuperVidel project by Nature. However, as it's designed for CT-6x upgraded Falcons, it doesn't need drivers as such (Falcon TOS 4.x supports it natively), so software would have to be written from scratch for it to be usable on a TT / MSTe. Also the SuperVidel is a highly complex design which is consequently very expensive - it's somewhat "overkill" for the TT/MSTe.
LP has suggested (over on the thread at Atari Forum) that an FPGA based ET4000 might be a good option, since NVDI already supports ET4000 on VME. That takes a lot of uncertainty out of the driver issue, though I've got no idea what sort of cost that would be - FPGAs are like the saffron of technology. So good and so many uses, but damn expensive.
Yes, I ordered one of the SuperVidel cards. But I was suggesting a *normal* non-Super Videl. Less complex, the TOS infrastructure is already there, backwards compatible with the old Atari screen modes, and a line doubler to get onto modern screens.