I was successfully able to create a LAGG interface with some of @LGA1150 custom builds, but it required a lot of hand tweaks to the config files and it would not work reliably upon re-boot. In one instance, I was able to increase the combined BW of two interfaces to approx 1.8 Gbps in iperf3 tests with my managed switch and three of my TrueNAS CORE servers, also configured for LAGG. The problem we were never able to resolve was bridging across the WiFi/LAGG path to the rest of the network.
Although, it would have been nice to get some more useful life out of the WRT series, the LAN side is not the bottleneck in my situation, the WiFi side is. After researching the advantages of 802.11ax, I felt I was better off investing in some new kit.