Regarding the longer wheelbase: It looks like they aren't using a dropped chainstay design, so maybe to increase tire clearance they had to stretch the rear triangle back?
Overall looks like a decent upgrade. I like that they went to three mounting bosses on the fork, but I'm not too crazy about internal brake routing on forks. It just complicates things if you have to remove the fork for steerer trimming or bearing replacement, especially if you have hydraulic brakes. With external hoses, you just snip off a couple of zip ties, undo a couple of bolts, and the caliper comes right off as a unit. No need for messy hose disconnections.
I kind of like the 15x100 axle on my current RDO for a trivial reason: I usually transport my bike on a fork-mount roof rack, typically on the passenger side of the vehicle. The 15x100 has the hex socket on the right side of the fork, so it's easy to install and remove the axle from the passenger side, and also you can keep your greasy hands well away from the brake caliper and rotor. I don't know if this is part of some kind of standard or if each manufacturer is free to flip the axles around whichever way they want.
P.S. For anyone looking for clearance prices on the old frames, also keep Competitive Cyclist on your radar. I got my RLT9 RDO frame there for $1500 about a year ago (retail price is $2300). I think it's an early 2018 model, or whichever year had the black/red/silver paint scheme.