I think a short course SC10 / Slash series is a top idea. It would be great way to get newcomers into the hobby too, with the realistic looks and handling. 10.5 motors fit the bill well imo. I also think it’s really important to keep strict control of tyres, I’d say allow the stock tyres from either of the manufacturers to be used on either truck, no mini pins etc.
In my perfect world, with the two current trucks (AE & TRX), I'd allow the slash guys 8.5 motors and SC10 10.5 to spice it up, make truck choice more difficult and balance the playing field. But that kind of stuff's difficult to regulate so one motor for all's probably best. It wouldn't affect me, I'd be last anyway