I can't think of anything that there'd be less demand for. You can get FF13 and F13-2 for about $15 each or less brand new. Hell you can get the CE of 13-2 for $30.
You know what there is fan demand for?
http://finalfantasy.wikia.com/wiki/Final_Fantasy_25th_Anniversary_Ultimate_Box
But of course that's staying as a Japan exclusive.
Know what else there's fan demand for? Remakes of 6 and 7, DS/3DS/Vita ports/remakes of 1, 2, 5, and 6, Type-0 getting localized, Versus 13 getting released, Bravely Default getting localized, A new Star Ocean game, TWEWY 2, a Xenogears port/remake/finished version/sequel, another Chrono Something game, a real Parasite Eve game, Dragon Quest 7's 3DS port making ti state side, a new FF Tactics game, even that HD port of FFX you've been teasing for 18 months. I can pretty confidently say any single item on that list is more desired than a trilogy pack of the worst two entries in the series.
Square, you wanna talk about fan demand, actually DO SOMETHING that fans want. Quit trying convince us that we want more FF13, we don't. Lightning is not as cool or hot as you think she is, Toriyama and Nomura, and as soon as the 13 "saga" ends everyone is going to forget she exists. Just make your Lightning cuddle pillow and be done with it, it's plainly obvious that the only reason one of the dullest characters in FF history is still getting the spotlight is cause Toriyama and Nomura want to give the old Eiffel Tower to Lightning.