As far as a new X-series body, I'd like one with IBIS. I really don't understand Fuji's "zooms get OIS, primes don't" philosophy. Stabilization is most useful for longer lenses. It makes no sense for the 10-24 to have stabilization and the 90 not to. They can rectify this without having to redesign all their lenses by adding it to the bodies instead. It would be like upgrading all of their primes at the same time! I'd also like a larger sensor, but not for a different crop factor, rather: for loss-free multi-aspect-ratio! (I mainly use my X-E1 with old adapted manual lenses, which are wonderful together with Fuji's retro film simulations, controls, and styling, so a full-frame sensor would be even nicer from my perspective, but I don't think it would make sense from Fuji's.)
It might also be interesting to have a new low-end model (around the level of the X-A/X-M line), but for a more sophisticated audience: keep the EVF, and lose the LCD instead; keep the same controls and styling as the higher-end models, instead of a PASM dial; and bundle it with the new 35/2, instead of an XC zoom. This would be aimed at people who are really into "the Fuji philosophy", but simply don't have the money for the higher-end models. I don't know how big this market would be, but it's currently a completely untapped one. The existing low-end models don't really cut it for this kind of potential customer, because they throw away the very things which make a Fuji camera desirable: if I want a cheap zoom and a PASM dial, I can choose from any brand on the market.
Finally, what I really, really want, would be a high-end, compact (as in small), semi-large sensor, constant aperture super-zoom: a Fuji response to the Oly Stylus 1. That camera is going on two years old now; technology has progressed. Target it for a higher-end market ($800-1000), and actually make it smaller. I think this is more feasible than it may sound: get rid of the awkward EVF hump, and have an unobtrusive rangefinder-style EVF in the corner like the X-E2 and the X30 instead, and rather than a built-in flash, bundle a clip-on like the X-T1 does. Also lose the tilt-screen, which adds considerably to the thickness. Now it's almost down to the size of an Oly XZ-1! To make even more space, completely get rid of the mechanical shutter in favor of a fully electronic one. With a 1/32000s electronic shutter, the built-in ND filter also becomes less necessary, which is even more saved space. It's a common trick to increase the zoom ratio or aperture of a lens, without making it bigger, by making it wider: for example, the Sony RX100 line went from 28-90/1.8-4.9 to 24-70/1.8-2.8. Along the same lines, a 24-240 equiv. f/2.8 lens should be smaller than the Stylus 1's 28-300 equiv. f/2.8 -- and probably more useful, too. With some of the saved space, we can upgrade the sensor to 2/3": keeping the image circle the same 1/1.7" size (so the lens doesn't get bigger!), but gaining loss-free multi-aspect-ratio. The result would be a camera with immense flexibility: 24-240mm equiv. with constant aperture, a decently-sized sensor, and multi-aspect-ratio, and very nearly pocketable! And that would be my dream take-it-everywhere camera.
(For anyone who still doubts its feasibility: if it was possible to produce the Stylus 1, then this should be possible as well, because it's basically what you get by starting from the Stylus 1 and, step by step, taking things out, upgrading the technology, and making the lens wider and shorter. The higher price point should also allow for more advanced miniaturization.)
