I personally don't think Bitcoin benefits substantially from having nodes within datacenters because that creates some centralization within the network as the node operators don't really have any control over it.
That's correct indeed.
Bootstrapping on Raspberry Pi takes a week or so, and assuming the HDD doesn't crash. That is about how much most users would spend to run a node. It is terribly slow but there really isn't a choice.
Imho it's a one-time operation and you basically just leave it running. I know that people don't have enough patience though. I don't know how good or bad it performs as node though.
On-chain capacity probably will have to be increased some point in the future. So it will become an issue sooner or later, provided that we don't do anything about it. Moore's law is more or less done for in the near future anyways.
This is the part where I can tell "please don't count on that". Since off-chain can bring the heavy load, I think that it's normal for on-chain remain restricted and expensive. If we don't do that we may end up with miners leaving when the block rewards get too small.