Hey @3D-Pangel - no shame in using only the free textures, in fact I'd recommend that everyone make use of them! Why not?
Indeed, Poliigon was founded by Andrew Price, who got started with Blenderguru. The team I am building up will cover most major 3D software, but it's not feasible that every developer to be an expert across all software, so we are being strategic about the software overlaps per individual.
As for your bullet points..... well, on all counts, let me just say you're going to love what we're working on (and why I'm seeking this developer)! The current addons haven't been advertised much which is sadly why you probably didn't see it, but that will change as we move into this generation of new addons. The new blender addon is further along (hence that "secondarily" line), but I want to kick the Cinema 4D development into high gear.
I also appreciate your point about utilizing the new C4D asset browser preview. That's going to be a focus of mine, making sure that every plugin we make feels native to each individual software, and not like it's just a copy-paste over between different 3D software.