OK, I'll bite. Since this thread was active, I think the Ultra4 guys have been making small improvement steps toward dependability and steering accuracy for faster speeds. HP has pushed dependable gearing to the limits.
On the steering side we are seeing more camber gain geometry in turns. Both IFS and SA. And on the straight axle hydraulic side, the hydraulics are much improved keeping a few on the 4400 podium. Most have designed out the rear steer on articulation prevalent in the early adoption of 4 bars.
Stock anything is now in the past. T400's with sturdy cases and 300m internals, Big brake rotors with 6 puck calipers, $30-50k motors, huge alternators to feed huge and numerous fans, KOH intended and marketed tires, $$$ Shocks, electronics, electronics, electronics, etc, etc. Every system seems to have been incrementally improved.
Not "proven" yet, but Portals are of big interest recently to try and open up the drivetrain gearing dependability, as well as a little more ground clearance.
We will see how portals work out. It seemed like the tech was started in Ultra4 but may be taken to the next level in Trophy Trucks. The Trophy Truck community seems to have more resources and $$$$ to improve on that game. Easily adding $200k to a build. ($16k single speed transfer cases, $32k Differentials, ???$$ Portals, designer time, ....)
So now the innovators are really thinking and I believe Ultra4 will be following the TT lead on drivetrain development for awhile.
Not all innovators are thinking portals. Not all want increased COG. Enter the thinking of 4 gear transfer cases. This opens up running the differentials on the correct side of the gears. Here is one example from Weismann, I believe.
Driveline shock from hitting rocks, landing jumps, ledges, braking, and etc.: There is some new technology being tested in driveshafts to absorb some of that torque. LIke a torsion bar. But that is just like coiling a spring. What will it do on the rebound?? That may have to be another driver learned reaction to the brake or other... Time will tell.
Everyone is cringing at the coming of an electric or hybrid racer. Right now there is about a 30% loss in HP due to the in-efficiency of all the gearing and slush box transmissions for dependable 4wd. Many thought it would effect the driveline parts manufacturers. But we are finding out that motors have best efficiency ranges also. And they don't like to be stopped instantly either. So for the designers, It might just be another game to understand. (If they can gear down a jet engine...a motor should be a piece of cake)
Sadly, I my opinion and experience as now building an IRS. I don't think it has a great future. You might have better control of the wheel but the grounding out (G-out) of the differential at full bump against terra firma HURTS and severely limits travel. (On the tech side it is really hard to control camber and axle plunge on the droop side of travel. As understood on Side-by-sides.)