Having FFV and FFVI on the DS would be the most sensible course of direction. The cost of development on the DS is much lower than on other formats and the time taken to develop for the DS would be much shorter. It would be much easier way for SE to fatten its wallet quickly without having to pour a lot into HD console remakes.
Besides, FFV and FFVI lack the notoriety and popularity of FFVII anyway. If there is to be one FF game that has the best (and most logical) chance of being remade in HD, it would have to be FFVII. An HD FFVII remake would inevitably reap more financial benefits for SE than either of its two predecessors.
Personally I think remakes are really unnecessarily. I know I've advocated for a FFVI remake before, and I must admit, it would be really nice to see it all in 3D, but it still doesn't make it anymore necessary to exist. The same goes for a FFVII remake.
Besides, FFV and FFVI lack the notoriety and popularity of FFVII anyway. If there is to be one FF game that has the best (and most logical) chance of being remade in HD, it would have to be FFVII. An HD FFVII remake would inevitably reap more financial benefits for SE than either of its two predecessors.
Personally I think remakes are really unnecessarily. I know I've advocated for a FFVI remake before, and I must admit, it would be really nice to see it all in 3D, but it still doesn't make it anymore necessary to exist. The same goes for a FFVII remake.