pretty much everything else - with the exception of hi-end industrial filaments - you can print on an open frame machine.

Also there's nothing stopping you from building an enclosure for an open frame machine. Few sheets of polystyrene and some tape is all you need.

Nylon is kind of tricky - no matter what. It really doesn't pay to buy generic cheap nylon. Go for something like taulman 645 or mymat (that's a bit pricier).
Both work well on unenclosed machines.

Other than that and not bothering with abs, it's all good :-)

for flexible filaments - I prefer flexible pla. It's slightly stiffer than tpu based filaments, just as strong and works well on both direct drive and bowden setups.
My direct drive machines will print flexibles up to 40mm/s, the delta with bowden only does it at 20mm/s - but given it's a full length bowden tube - it shouldn't be doing it at all :-)

I do have good soluble filament , but as I design all my models to print without supports - never really used it.