Beamforming is basic GCSE physics, adjusting the phase of 2 signals to adjust the interference pattern to produce a peak signal at the required location in the wave pattern. Outdoors this works brilliantly, predictably and significantly extends range without increasing transmission power. in a house many with signal blocking walls it may be harder to achieve.
In fact it's so simple, it a why didn't they do this sooner kind of thing.
My advice would be to get a RT-AC68U when it's on offer and use a separate modem ( this leave room for future broadband upgrades while being able to use the same router ), or keep your existing setup and buy and slightly modify the settings of somthing like cheep BT home hub 5 off e-bay to use as a AC wireless access point.
The latter is the cheapest way to get an wireless 802.1AC access point. regardless if your lucky enough to be able to get an upgrade, right now nothing short of a moderately fast PC acting as a router can realistically handle over 300mbps internet with full firewall protection and even the very latest routers cannot handle a full duplex gigabit connection and give full speeds even with cut through NAT which bypasses much of the firewall capabilities of a router.
Edited by Ragnarok (Wed 16-Mar-16 10:28:16)