Technology wise, the R/S/E remakes isn't an option considering the graphics were quite advanced after the original G/S/C games and also not too much different from the new ones. The graphics of the new ones are more advanced than the R/S/E obviously, but not merit enough for a remake. Even though Sapphire is my all time favorite game (story, geography, the Pokemon, and Elite Four), I'm not wishing for a remake at this time.
As for 5th, to be honest not sure if there's going to be one, considering many people saying Arceus is pretty much the end of the Pokemon line. @_@ However, if there is going to be a 5th gen, the people better make a bang! XD;
If there were to be both, 5th gen first and then the remakes.