I feel like the watch becomes a platform, much more than it is today. Certainly in the Far Future anything could be a “platform,” that is, a something that hosts different modular and extendable capabilities, but I suspect that even then the best platforms will be ones we’re used to (eyewear, watches, jewelry) and ones that are just very convenient (implants).
The platforms can all “talk” to each other, one of the aspects of being a platform. The watch talks to the eyewear, and the implant, and the ship, and the external net, whatever that happens to be. There are protocols, safeguards, and so on.
Style, fashion and form are still a thing.
Perhaps there’s an “anchor” platform device, one that drives the rest. Right now in our world that’s the mobile. It feeds and accepts telemetry with the smartwatch, or the FitBit, and the car. I suspect in the Far Future anything easily worn of implanted can be an anchor device, or maybe all of them and none of them are, each sharing and providing redundancy.
As for interface, really the sky’s the limit. There is the discreet real estate of a few cm^2 of the face, but that’s just where you start. Haptics (the vibrations, etc), the tones are axes along which information can flow; in the show The Expanse you see people flicking data, files, and whatnot from one device to another (say, from a watch to a large wall monitor) to get a better view, or show everyone something. In the future there will be other interfaces- links to nerves stimulate emotions, images, sounds, and so on that only the wearer can perceive.
Jon Watts in his Clement and Earth Sectors setting has cool hand comps that do a lot of these things. The next TL jump there, it’s the size of a ring, and the next it’s something implanted. All are platforms that you can add functionality to. In addition to the above they can project holographically.
If I were creating an NPC, a seasoned Scout let’s say, and I didn’t go the way of straight analog mechanical just to be anachronistically cliche, I’d say her watch could do these things:
- Serve as an anchor device, communicating with all other anchors and external systems
- Could add/extend functionality
- Did biomonitoring (because it’s actually in contact with her body in a point that facilitates such stuff)
- Store personal data - her ID, credentials, certs, licenses, keys and so on. Pass them on with a flick or other gesture.
- Provides a convenient audio communication focus (a la Dick Tracy), whether it was doing the communicating or tethering to a device that was, or both
- House environmental sensors that’d be handy if she didn’t happen to be wearing a vaccsuit. She could get information (a certain turn of the wrist reveals the temp, on the face) or receive a telltale haptic signal if there was a pressure/rad/moisture delta
- Also along these lines, it’d be the main “communicator” of things like messages received, bio and environmental changes, and other telemetry simply by virtue of its location, and always being worn in a way that facilitates a lot of different kinds of subtle information passing. Forget having to fish a mobile out of her pocket. The eyewear (if present) gets the stuff more suited to visual scanning, but I can imagine a lot of useful data that could be transmitted with just haptics, tone, the face, and maybe a temp differential. These cold be inputs from other systems, that watch is merely a conveniently placed way to pass the info.
- IMTU, Scouts have an eclectic culture; the watch would say something about the wearer - postings, time in, farthest place been, and so on. It’s a point of conversation between those who know, and often a conscious addition to the gear carried everyday.
- Heck, it even tells time…
For me and in my games, power and storage are non-topics; solved problems.