I've been thinking about it, and even though I'm still helping out with another Pokemon fangame currently, I'd still like to help out with this - the idea has just gotten too enticing for me to pass up. :P
I've yet to play ANY of the Digimon games yet, but I have been sticking my face in the DMA Digi-Dex (bookmarked on my Firefox) for the last 2 weeks or so just because there's SOOOOOOOOO many Digimon I didn't know even existed.... So, ideas have been going through my head constantly. Even though I don't know if these 2 ideas has been done before or not in a previous game yet, but there's so many Armor Digimon available, and, if this is going with the Tamer thing, maybe a select Digimon that can Armor Digivolve (1 of the 5, obviously, unless you're intent on making others) could headline the Tamer's party. The other, ala Pokemon Ranger, a Tamer's Digimon can do something in the overworld that another couldn't, for use in particular circumstances; however, something tells me that that idea HAS been used in official games already.
Keep in mind that I've been out of the loop for quite some time.