I agree with your thoughts. I would like to perhaps see a mother board approach to the rig. A set of basic modules:
receive input bandpass filter
transmit driver stages
transmit final amplifier
transmit low pass filter
that plug into a mother board for inter connect. Add to that prototype boards that would be used to replace various modules with other implementations for experimentation. Maybe provisions on the mother board to add an Arduino to control a DDS replacement for the VFO, a display, keyer etc.
Basic package would be simple modules to get a working radio. In some ways this would be a modular kit something a bit like the Tentec Rebel. Maybe even have provision on the mother board for a balanced modulator/filter for SSB generation some time in the future. Perhaps a partial chassis for the rig could have a front panel big enough for several knobs for various controls and a display.
Maybe a place on the mother board to plug in a tuner module. The whole package would not be super small but rather large enough to be able to easily work on (and build).
73/72 - Mike WA8BXN