Focus on MPCNC, because there’s a new 3D printer every 20min :=)
The Itopie exists already and match all of you goal (with a lot of option, prusa i3 compatible, a perfect documentation, tested and corrected by a lot of people, totally customizable with generator…fast to print, to mill and to build…). But it’s still a cartesian, a perfect printer for beginner, easy to build, to understand, but a bit slow. Or continue to make your own one, like we all do, because we all have different needs. But it takes some time to do a 3D printer from A to Z (we are human -> mistakes, try again, etc…)
I’m not agree with what you think about bowden: my bowden is short, the Gunstruder push the filament without grinding it, with muuuuch more torque than all my precedent extruder (mk7, mk8, direct, wades, beast_reprapworld_hobbed_bolt, etc), the motor stay cold, no stringing, no oozing…My printed parts for the MPCNC took me half the time you wrote and they are clean and strong (and I printed them slowly to avoid any mistake). I can print everything (soft filament, etc…).
It’s not just about mass and inertie moreover: 2 or 3 motors running almost always together have more torque in average. I read an article about that from a mathematician, but I don’t remember what is was exactly, but in conclusion of the article : delta could be faster, then corexy, then cartesian (from what I remember).
BUT! It took me a lot of time to make my corexy to work perfectly, and I had some experiences already. The BOM is long, the build was long, the calibration long, etc…It’s not perfect….