Just got the WRT1900AC, interesting piece of hardware. Seems fast and stable, very solid, and I'm impressed with the level of testing that Linksys/Belkin has done when I compare the stock firmware with my experience with the R7000 stock firmware.
Haven't time to do performance testing yet, but very happy with the fact that I can reboot the WRT1900AC and not lose my internet connection with IPv6 enabled. I'm not sure that Netgear will ever get right. Also, all computers, smart phones, and my iPad also work with IPv6, another thing that Netgear doesn't get right. Some wireless devices don't have IPv6 available using the R7000 with stock firmware.
The WRT1900AC works with all our devices, getting an 867Mbps connection using the Asus USB-AC56 adapter, works with phones, tablets, ethernet bridges, MoCA, etc. No problems yet.
The only thing I don't like about the WRT1900AC so far is the lack of features in the firmware. This lack of extended features that I expect in a $250 router makes it easier for firmware developers to put out nice, stable firmware, but leaves you feeling like you didn't get what you paid for. Even the Netgear stock firmware, as much as I don't use it *smile* has a bunch more useful features. Although the stock firmware for the R7000 comes up short on features, as well, and has stability problems that I haven't yet found in the WRT1900AC stock firmware.
Another minor annoyance is that I've spent some time looking for an "uptime since last reboot" clock, pretty much standard equipment in routers these days, no luck yet. It is helpful to remind you when you last had to reboot to get a feeling for long-term reliability.
Anyways, I don't know if Linksys plans on adding more features to their firmware over time. However, I've seen clear statements in the documentation that they intend to support the development of open source firmware (not support the firmware, just the development *smile*). If I could use dd-wrt firmware with this router, that would be a great combination. Just like dd-wrt makes the R7000 into a great router, it could do the same for this one. Got my fingers crossed that this gets done.