5$ per month while you control your own money seems good for me. You definitely pay more to your bank and you do not control your money. Also this issue is only for US (I guess). There are places where internet is cheaper and places where internet is more expensive so this 5$/mo doesn't apply to everyone.
Exactly, in countries where bandwith costs a lot, full nodes will tend to disapear.
So we will start to make holes in the mesh network.
For pending questions
how much security do we need ? It's hard to quantify security:
I think we should be ultra conservative and try to reach maximal possible security level.
Don't forget that those who have potential to kill bitcoins are not Trolls...
For
full node decentralisation, what to say? incentive and keeping costs as low as possible would work the best. (the more, the better)
blabla
one blockchain record archival solution doesn't work because how would you find the longest cumuled diff chain with only one chain? No way to know if it's cheated...