I'm far more concerned about the security of the network being impacted, instead of the issue surrounding the costs of a full nodes. In this day and age, most people simply wouldn't opt for a full node as their daily driver unless they're interested in Bitcoin. Most people wouldn't run a node, no matter how much money they can save simply because it is time consuming and not very rewarding.
The miners are the ones securing the network and I think most of them can easily afford to buy more storage/bandwith. In this regard, less people running a full node isn't really a threat...
The issue surrounding block size has really been discussed over and over again and I doubt we would reach a new conclusion by doing it again. Again, since this issue brings us to whether we scale on-chain or second layer, it doesn't make much sense to discuss it on this thread. I prefer the latter, 100MB blocks isn't really desirable for the near future.
If the demand for block space increases more than the supply then eventually the transaction fees will become so high that only the rich could afford them. Here's the problem and one solution..
In theory, the sender does not have any incentive to pay more than the "min fee" if there's no excess demand as he doesn't have to compete against other people for block space. If there's an excess demand then the block size limit willl determine how many transactions will pay more than the min fee, therefore the block size limit and the avg transaction fee are inversely related. We can balance the supply and demand with this simple equation:
new block size limit = previous block size limit
x (current avg fee / previous avg fee)
We know that the avg fee depends on the amount of transactions that are waiting to be confirmed
AND the block size limit, the demand for block space shouldn't change much in the short term.