I use OpenWRT and what I have wished for is a configuration file as robust and simple as the one for pfSense. Version upgrades amount to a migration headache.
Also, I think the configuration file is already robust enough; you can edit them using a text editor like vim or edit them using the UI or edit them using the CLI tool. I cannot think of anything to make the configuration file even more robust.
At least on the hardware I've owned, OpenWRT has to be reconfigured after version upgrade or else it becomes unstable.
Thankfully all the config files are plain text and can be manipulated however you like. It is usually not too difficult to take working config while fixing or disusing problematic files.