I ran third party firmware on routers before it was cool to do so. I ran Sveasoft (I think DDWRT was a spin off) on my 54G and 54GS back in 2004/2005. Yeah some of the additional features were cool, but I would rather have firmware that was developed by a team of paid professionals, then what I assume are just a bunch of open source volunteers. My router probably has more features stock than third party solutions have, features that I don't use or can even begin to understand. With third party, non factory supported solutions there is no expectation of things to work.
I don't consider dual WAN or tunnels hardcore for home use. Niche? Yes, for sure, it's stuff your average bear won't touch, but it's not totally unheard of to use in a home setting. Before gigabit fiber and cable became as widespread as they are today, enthusiasts were bringing in two fiber or cable subscriptions into their home and using dual WAN routers to bond them. I can load balance or fail over between four WAN sources, two Ethernet and two USB for cellular if I desire. If I had cellular reception I'd have a USB air card instead of HughesNet. Since my cable node is not backed up by battery I lose internet, landline phone and cell phone (on wifi calling) when the power goes out With dual WAN, as crappy as HughesNet is, at least I have internet and phone for as long as my battery backups last. I've seen enthusiasts who have two homes, who are snow birds or who have weekend cabins use G2G VPN tunnels to share files and media from one location to another.
What I consider hardcore is those that have dedicated full blown PCs that act as routers, have 10 Gb NICs in them, and use LAG on cable modems to achieve 1 Gb+ speeds. I've read online of people on gigabit tiers from Charter and Cox who do this, just so they can achieve the full overprovisioned 1200 Mbps as opposed to 950 Mbps