It's more than a dial or unique slant on display, I've been more on features that go beyond modding. Things that make a watch do something, or help the user in a new way.
Jotting them down here, maybe we'll see these some day.
Externally adjusted regulation of automatics: really a no brainer, we've got all sorts of pushbuttons and the stem perforating the case already, even in Dive rated watches. So, sealing it against water ingress isn't the issue. A simple recessed screw head in the side of the case attached to the regulator would make it dirt simple to adjust to a gnats hair of accuracy. Just not flat or phillips, please. It's just another stem with a worm gear engaged to to a rack on the arm to slow the rate of adjustment.
Bracelet clasp UNDER the case: We've dealt with bulky clasps with layers of strips bunched up under our wrists for decades. This can be made much more low profile with "halo" rings that nest under the case, hinged the same to expand the circumference of the bracelet for removal. The locking clasp integrated between the lugs - which would make the folded end link more justified, it's the foldover clasp. Somewhere we could even have ratcheting adjustment for those last 4 to 5 micro increments. 1) Flip up end clasp, 2) pull up watch case to unfold the extension, 3) unfold the second leg from under the case, and remove.
Minimal case lugs with mineral glass bubble back: Just another extension of existing tech. A complete hard mineral glass case back that drops into a case ring just big enough to have lugs and a wind stem tube. Press it, or have the upper bezel mounting ring screw the whole assembly together. I'm not ready for actual glass lugs yet, but, who knows? This would get you a completely exhibitionistic case for that overwrought decorator movement - or at least a watch show timepiece for display.
LED indicators: We've already got "chapter ring indices," those sculpted rings that stick out into the hand space that look like inverse gearteeth telling us the hours. These are getting bigger, multistepped, and offer a lot of visual appeal to the flat dials we've seen. Might as well add LED's, small ones with limited output, command lit, or that can glow controlled by a light sensor. The kick is how to power them, obviously a solar charged and/or kinetic powered battery (separate from the movement.) Low power consumption, low output. LED's won't suck power from a battery that badly, 'moon' mode on flashlights is measured in days, now, and some red dot optics will go literally years left on. I suspect they flutter the LED onoff about the same rate as motion picture film to reduce power consumption, It gives the impression of always on, while actually being mostly off. And fiber optic hands aren't that hard, that works in a lot of mechanisms.
Corrosion proof movement: This won't go over well with makers, but they've been doing it to us far longer than we should have tolerated. Geartrains made of rusting steel parts is planned obsolescence, quartz movements with bare conductors are a new watch waiting to happen. We know to make the case water "resistant," but the internal parts should be more so. Consider that we have carbon fiber dials, polymer date rings, and stainless parts galore already used. Let's just push it a little further - 316l, tungsten carbide, delrin, etc, much less the superexotic polymers out there. I'm not advocating plastic wall clock movements, but reducing the inertia and mass of the works makes them more shock resistant. Horribly enough, the more reknown beaters use - ahem - movements typically considered for cases in the dime size category. If sea water gets into your watch, why does it become economically unrepairable to replace the movement? So they can sell you another.
Completely sealed case: It's just the next step away. We have 5 year batteries, stack two, it's ten year, the life of a lithium in storage. Add atomic time adjustment, voila, no stem at all, even analog. Epoxy the case shut, when it quits working, toss it in the recycle bin.
Maybe some of this has already been done, it wasn't mainstream or got noticed. But, if you like to, build it, there's plenty of room in the market for something new, and better.