A journey worth to watch:
What is your opinion about using PD for this type of project
I would not use PD for a hardware product like this. Even less if I would start all over again.
The community is small: In the future, the pool of people you could hire would be small.
The documentation could be better.
Even the graphic account is falling a bit short for a patching environment.
And there is a lack of debugging-tools.
While you are struggeling to solve how to get midi-i/o without jitter around the block-boundaries of 64 samples, there are popping up tens of new AI libs in Python.
embedded linux based project, most probably ARM cpu
This might change in the future, as technology moves on
Also resources wise?
PD has overhead, but is running on such a board. You can do very basic multithreading.
The reason why someone would buy this, is it's open architecture.
Also related to the quality and diversity of the tools available?
Also related to the protection of the work, is there any solution to make the project "closed" ?
These are two conflicting statements in the PD-world, imho. And once again, having a closed design in mind, I see no reason of using PD instead of more popular languages.
Libraries have different licences. For example [expr] has a different license than PD-vanilla.