sfx2000
Part of the Furniture
Depends on the manufacturer of the SoC probably, maybe they switched from Marvel to a new platform whose 802.11ac platform uses a 1.3 GHz CPU. Also, this router is newer by a year, so probably the SoC is newer as well.
Looking back at the WRT1900ac, the big stumbling block was the Marvell wifi driver, not the actual SoC - Marvell's support there is without question - it was the WiFi that they would not release a GPL compliant drive...
Looking forward to seeing the board shots/bill of materials...