Other than the most obvious issue with the filament kinking in the tube, what other issues could arise when trying to print flexibles (i.e. TPU/TPE, Nylon, etc.) with a Bowden style extruder setup?
Can the kinking issue be alleviated by a well-constrained filament path (proper ID) in a properly sized Bowden tube?
As a user of an UM3E, which uses Bowden tubes and has TPU as an available material, I can tell you that the kinking issues can be alleviated or downright avoided.
I've printed quite a few things with the Ultimaker-brand TPU 95, and never had problems with kinking in the tube.
Ultimaker uses 2.85 mm filament, with Bowden tubes adapted for those and a rear motor, i.e. the motor is on the back on the printer and not right on top of the print head.
I personally wouldn't consider Nylon as one of the really flexible material, but that's my opinion. Never had kinking in the Bowden tube with Nylon either in my UM3E.
To also validate the first answer, I have been printing with TPU95A for a number of years and it has been one of the most reliable materials to use. The strength of the product alongside the flex makes it a test and production based outcome with fewer issues. My printer for the most part of this experience was the Ultimaker 2+ that has a similar set up to the UM3 with a more traditional hot end.
Cautions: Some older material profiles have the heatbed at 60c. I have always had better outcomes from room temp (no heat on the bed).
