Next: AWD pickup - most parts stay the same, just have to redo some things under the hood and with the front axle.
Next after that: 4 door pickup - as above, most parts stay the same, but maybe have to stretch the frame some.
I sent them an email asking about this specifically and got this back on 5/16:
It's not a guarantee but if they do this, I'll buy one. It would literally be the only pure BEV option!
Caveat: Rivian also planned for the R1T to be flat-towable up until close to the release date.