There is very little chance that iPSCs will became cancerous.Of course, no one wants to implant mutated cells, not only in japan they want to avoid that.
You have a thing called scar tissue, I don't know if hair transplaints can handle scar tissue, so if you already have done some procedures i don't think the "endless transplant" idea is going to work.
But high density is a problem in relation to blood flow, it have been shown before, and high density we are talking +200 pr cm2 and not the 60 - 70 pr cm2
Plus, in 2020 there were couple of breakthroughs by scientists how to clone iPSCs without spending months in labs.
Customized programming of human stem cells
Induced pluripotent stem cells (iPS) have the potential to convert into a wide variety of cell types and tissues. However, the 'recipes' for this conversion are often complicated and difficult to implement. Researchers have now found a way to systematically extract hundreds of different cells...
www.sciencedaily.com