Just a comment from enduser perspective.
( I already struggle hard to get my small wiring project organized. "cable management"

)
Diving into "building Linux from source", and fighting drivers etc. seems to be completely unreal.
Most (or only some?) people already having a hard time with the hal configuration and getting basic UI functions to work.
How many thousand hours do I have to spend extra in sofware research and learning new things, in order to save 60 coins on a control card?
Considering the cost of mechanical components (e.g. for metal working machines), the FPGA card is the least financial problem.
I feel that leaves a very small target group beeing interested in a "race to the bottom" with FPGA card pricing. This target group is also looking into 3d printer firmware and hardware. (cheap, and for some things usable)