Do you think simple, Linear FM is possible with DCO's? Specifically, Osc 2 modulating Osc 1. (Even though there're no sines.)
That would be a little feature that I think would be quite unique, and exciting. Even if it was hairier, as it's not a precise digital oscillator. Basic DCO, 2-op linear FM. It's very primitive FM, but I imagine it to be useful.