I suspect that such a signal generator would be of limited utility, with the possible exception of audio work

It should be pretty easy to implement, though… you could use one of several cheap I2S decoders like
this one in conjunction with some kind of MPU like an Arduino or STM32 and an audio amplifier to output waveforms up to ~45kHz on two channels based on whatever arbitrary data you can either synthesize in software or play back from memory.
The problem is that for about the same amount of cost and effort, you can probably put together a respectable signal generator for common waveforms (sine, triangle, square) between, say, 0.1Hz and 1MHz using a dedicated DDS chip like the
AD9833 and a couple of cheap op amps like the LM318. With slight better parts and design, you could probably stretch it to 10-12MHz. You lose the ability to generate arbitrary waveforms, though.