I dislike BIP100 only because it is not a long term solution and it guarantees us to have this debate all over again unlike BIP101.
Nope. Even though there is no real evidence that this was said by Gates, here it is:" 640K ought to be enough for anybody" (referring to RAM). Gavin said something similar with 8 GB blocks.
8 GB blocks do not guarantee a permanent solution. You're just speculating,and so is Gavin. Trying to predict stuff (in addition to not having solid evidence; not saying that this is the case here) is pointless as most of the time the prediction ends up wrong. The bigger time span you try to predict, the worse your odds for being correct are (good luck trying to predict what will happen 15-20 years from now).
It is fairly easy to estimate how much transactions can be handle by a global usage. It's not that much speculating but yes, it is still a limit but at that point alternate solutions (AKA lightning and sidechains + shared market cap of other major altcoins) can come into play. 8 Gb is fairly enough to ensure a great amount of transaction fees to keep a large incentive to miners and ensure a maximum network security.