I found this guy’s approach an interesting way to keep the Bowden tubes short on a delta printer. Watching the thing move, bit concerned the wobbles in the pivoting extruders might get transmitted into the frame, or tug on the printhead - especially with fast prints.
Liked deltas quite a lot, until I started to think about fast, large prints with multiple extrusion. Direct drive would mean a lot of mass on the print head. With a Bowden style extruder the mechanical properties of the various filaments affect your print settings, and rather a lot for long Bowden tubes - not a good thing.
If we modify this approach by mounting the stepper on the truck (on the rail at the end of each arm), the Bowden tube is short, with minimal changes in geometry. Fabrication is simpler. With a geared extruder we could use a lighter stepper.
Odds are someone has tried this before, just not something I have yet seen. 
https://www.youtube.com/attribution_link?a=2WichEloEpo&u=/watch?v%3DPOsKLbXNbZ8%26feature%3Dshare