I wasn't even aware there was such a thing as a "floating-thumb purist". Unreal.How many people actually play bass without anchoring their thumb somewhere - that is, they play with their hand floating in free air, with only the plucking fingers touching the strings? Are you advocating for a classical guitar-type technique? If you have a special technique, fine, but calling the technique that most bassists use a 'deficiency' is quite a stretch. I have come across 'floating-thumb' purists regularly, but this is a step beyond...
I'm gonna start the "one string movement". After all if you need more than one string it is because of a technical deficiency.
To go back on topic, as I was building a 3D model in Sketchup for the thumb rest, I realized that there are several ways not to drill the body while still coming up with a solid thumb rest that doesn't rotate around.
You can use the lateral support of the pickups, the one pickguard screw between the pickups AND the 0.5 mm gap between the bridge pickup and the body of the bass. Of course this is almost impossible to build without a 3D printer.
But I'm also realizing that for my playing style I can get away with something like this.
Right now I temporarily attached a piece of plastic to the body to test how long my thumb rest really NEEDS to be.
It's interesting to notice how important it is that the thumb rest is well rounded and feels good to the thumb, otherwise it feels like something extraneous that I don't really end up using.