Custom router bits do exist for the track groove profiles, which suggests that SOME folks are doing it. I've always wanted to create some custom pieces--my siblings and I growing up played with Brio far later than the expected ages, as we were all railway nerds, and frequently mis-used the degrees of freedom of track components for wildly more complicated layouts spanning rooms.
Nowadays one of my nephews ended up with lots of generic track (gifts from uncle: me) and some very specialized custom switches cast out of resin by his maternal grandfather. There are multiple ways to solve the problem!
Lidl and Ikea wooden tracks are pretty cheap and mostly compatible (you might have to file the joints a little, otherwise they can be hard to attach and detach).
Lidl & Ikea tracks give a feel of cheepnis. I haven't stopped to properly contemplate why it is so. Maybe some sanding of edges would help - Brio are much more pleasing to the touch.
Nowadays one of my nephews ended up with lots of generic track (gifts from uncle: me) and some very specialized custom switches cast out of resin by his maternal grandfather. There are multiple ways to solve the problem!