I think I'd like to keep my knees...do you think there would be a way to almost "re invent the wheel" and make a split capable of skiing and riding normally?
I don't see how. If you had a sidecut on the inside edge, it would ride all kinds of fucked up. The binding issue would be pretty tough too.
I don't see why you'd want such a thing to be honest. Buy skis for skiing and boards for riding. Splitboards only split for the hike up. There's no intention for them to be used as skis on the downhill.
there are some 3-piece splitboards (i don't think any commercially) that have been made where a middle section is removed and carried on the back to make two more ski-shaped skis.
it might be possible to make some kind of setup like this with hardboots and some kind of AT binding to do what you're asking but in reality it is pretty stupid.