What kind of improvement is still to be expected?
AF performance: sure, room for improvement
Dynamic range, color acuity, high ISO noise? We've pretty much plateaud for single exposure image quality. Any significant improvements with the current silicon-based technology will come from computational / stacked exposures, which highly benefit from faster readout speeds, so that's a shared interest with video requirements.
Body styles / handling? We're seeing rationalisation rather than experimentation and wide ranging options to suit various preferences (for stills cameras, at least; action cam / vlogging cameras are in a highly experimental phase right now) so this is unfortunately not an area in which I expect much progress; more likely regression unless you're lucky in that your preferences and a manufacturer's chosen direction align.
What else is there? Workflow? It's not improving rapidly, unlike all the supposedly wonderful AI based image improvement software, which the purist in me dislikes but the pragmatist in me admires.
Am I missing any major fields of development? Perhaps one could count weather sealing as a field showing some improvement over recent years, as well as (mostly video aimed) connectivity ports.