I have been thinking about the same question. I have an old Wheely King and a heavily modified clod. They are both a lot of fun, but require lots of repairs and maintenance. Given the upheaval in the industry (companies merging, going out of business) I agree with your feeling, which is that parts support is the key issue these days.

Given that the axles and drivetrain are the heart of the MT, my plan is this:
-- get a TRX-4 roller (axles, transmission, links)
-- eliminate the portals (portal delete kit from SSD)
-- get a one-speed conversion for the transmission (no need for 2-speed with modern brushless+lipo)
-- SMT10 chassis
-- proline shocks (although traxxas would be fine here as well)
-- eliminate the remote locking in the rear for sure, undecided on the front (not sure about durability)

That would give you a Traxxas driveline all the way through, and I like their parts support and aftermarket support.