So it appears that Marvell pushed a bunch of patches to OpenWRT on Christmas, and as a result, trunk OpenWRT (kernel 3.18) can run, and run pretty well, on the 1900AC.
dual-core 1.2GHz ARM. Given my experience with processors like the iMX 6, this should be light-years ahead of the WNDR3800 in terms of CPU performance. Perhaps this will let the sqm scripts go well above 100Mbps?
-Aaron