It's entirely possible that these two ideas have already been suggested, but I don't really have the time or energy to comb through 156 pages of suggestions to check. The first of these, I feel is sorely missing, and the second would just be a great feature to have given how beautiful the game is......
1) Some way to preview housing items before buying them. Anyone who's ever spent money on furniture knows that they can be quite expensive to buy off the MB. The problem is that right now we only have two options to view what furniture looks like, barring the tiny item image. Either buy it and then try to place it in your home/apartment, and hope that you can resell it to regain some of the cost if it doesn't look good. Or see someone else who has it/go looking around the internet to find a picture of the particular piece of furniture you're looking for. What we need is some way to do a preview for it from the marketboard/crafting menus, in the same manner that we can preview gear for our characters. I would also recommend having some sort of feature within the preview to show the scale of the item, such as showing our character model in the preview, or an apartment sized room.
2) Minion - Magitek Camera - A floating camera minion that you can summon and have follow you around. When you use the group pose, idle camera, or temporarily hide the hud, the minion becomes invisible, and allows you to press a button/key to allow you to take a special screenshot that can be used as an in game decoration. The idea behind this is simply that the game is beautiful, and many of us enjoy capturing moments from time to time. These moments would also make for great decorations to put up in our homes, because they're more personal memories than the standard paintings available in game. As for why a minion? The idea there is that it will make it so that the screenshots taken with it are directly from the game itself, rather than just whatever pictures the player has on their hard drive. This both prevents inappropriate images, as well as breaking immersion from the game by having images from other games/media. Some other possible ideas for it are including a limit of maybe 10-20 pictures taken that can be converted to paintings, in order to reduce data usage, and to have the actual "paintings" be acquired by speaking to the painter in Idylshire and paying him a small fee, (maybe 10k gil), to "commission" him to paint it. As for why a minion, and not simply an option in those to begin with? Well, two reasons, one is so that you have a button prompt visible so you know what to press to take the picture with, (mostly for players who wouldn't use the feature that often), but without it always being present when you simply want to take normal screenshots, and the second reason is just to add a bit of flavor and have it be immersion friendly.