[wtallis]

Pretty much the only custom code that router vendors write is the web UI, which is sometimes a fully custom job and sometimes a reskin of DD-WRT or OpenWRT's web interface. Otherwise, they're generally shipping whatever code they got from the SoC vendor, which is generally a fork of OpenWRT from around when that SoC taped out.

"Use open source" would make the situation appreciably better, because it would mean not accepting any closed-source or out of tree drivers that lock you in to particular kernel versions and non-standard management APIs. Once those problems are out of the way, frequently rebasing the web interface on current upstream OpenWRT is pretty straightforward.