The Netgear Nighthawk r8000 is Broadcom based, but its fullmac Broadcom BCM43602 wlan cards are supported by the mainline brcmfmac driver, which is fully supported by OpenWrt. Most other Broadcom based routers are using softmac based Broadcom wlan cards instead, for which the driver support state would be between poor and non-existent.
While the device is fully supported by OpenWrt and relatively powerful, it's still a rather rare device within the OpenWrt ecosystem, meaning that while it is supposed to work long term, it doesn't have as much of a community around it (who tests it, reports bugs, maybe provides patches where necessary) as the more common devices using different SOCs/ wlan cards. You also need to keep in mind that while it indeed has three radios, the two 5 GHz wlan cards are tuned to different sub-sections of the 5 GHz band (the lower channels, as in roughly 36-64 and the upper channels from roughly 100-165) and don't work (well enough) outside of their intended frequencies.
IMHO its RAM size doesn't really qualify for an enthusiast level device anymore, but if you're fine with the radio limitations (frequency bands) and can find it rather cheap, it might be a pretty good option (the SOC is rather performant and has pretty good mainline support), but you need to be aware that you might have to invest a little more effort in case of problems than for other devices (which are more commonly used for OpenWrt).