i have played FF14 on the PS3 and it was HORRIBLE. i wished they had never released it for that plattform. couldn't wait to get my hands on a PS4. this game is clearly designed with the PS4 in mind and it is not really working on the old PS3. endless waiting for summoning retainers and NPCs, you can't see most of the people in crowded areas, HUNTS, i had an hardware delay and it was impossible for me to dodge some AOEs (on the day i got my PS4 i was suddenly a way better player xP)...
if the game was working in the PS3 but holding the other plattforms back i would say: nope, don't drop PS3 support - but it isn't working. the game is horrible on PS3, so they should drop the support to get rid of the mess xD