I agree it would get more complicated, but there are some nice things we could get with text. For example, a “turn right heading 320” or “proceed direct BUXOM”

I agree it would get more complicated, but there are some nice things we could get with text. For example, a “turn right heading 320” or “proceed direct BUXOM” could become a popup on the screen, which can then be pushed straight to the FMS with a single press. The plane could also report its active flight plan and mode (i.e., whether it’s tracking a course or following a heading) which would confirm whatever ATC expects the plane to be doing. There’s a myriad of downsides to this, including bad actors sending instructions to pilots without ATC being aware, so in balance this might be overall worse than just keeping it simple.