Visible on Voyager by tapping the image

overall we need something to text

pretty much Matrix’s entire point

(plus send files)

also implemented in pretty much every server and client; I think even Element can send files

call

look into e.g. #matrixrtc:continuwuity.org — sable requires a setting to show the call button in non-DM rooms

video/screen share

unfortunately this is the only thing I’m not confident is supported

bonus for emojis, stickers

should be available with any im.ponies-compatible client such as sable

Not telemetry? Continuwuity just uses it to post release announcements to the admin room; I think there’s a way to disable it if you prefer.