has 4 pins that seem to be a serial connector (didn't try yet)
Would love to install openwrt on this router ; worked on the WMR-300 (contributed to the page to get OW working) and Buffalo are quite consistent in their firmware design, so that would be a plus.
In terms of lexra (Realtek's reduced mips ISA) support, there is none - nor anyone actively pushing for it (as in providing patches/ pull requests against current master); chances for this to change are non-zero, but extremely low (once you'd have hypothetical lexra arch/ SOC support, there would still be the problem of the wlan drivers and current hostapd/ nl80211, to drive them reliably in AP mode).
[Disclaimer: I can't speak for the LEDE/ OpenWrt developers]
Personally I don't think lexra will 'ever' be supported in LEDE/ OpenWrt (too different from normal mips, no upstream/ toolchain support at all, very low-end devices, the wlan situation (drivers, AP mode reliability, nl80211 support) is difficult). But effectively all it would need, is someone pushing for it - to provide a (long-term-) manageable pull request with lexra support against OpenWrt/ master, kernel 4.14, musl, hostapd/ nl80211 for the wlan drivers and not too many arch specific changes (so it can be reasonably updated with the rest of OpenWrt and not stay behind).