As I said rather than trying to figure out the international treaties, I rather look to what is happening on the ground in terms of lawsuits and whether companies are actually complying or not. Chances are if the companies lawyers deemed the best option was to comply then the local laws are having some impact and this will always go from big fish first to the little fish because of the amount of money involved. The EU law change that would concern those even with online only businesses that aren’t based in the EU occurred at the beginning of 2015. The current broken link in the chain for the most part is that the IRS and the EU tax authorities when it comes to VAT aren’t cooperating, or at least not fully cooperating. In lawsuit terms only being a year and a half into this law is quite young but when U.S. based companies with no physical presence in Europe are starting to collect VAT I think it’s clear which way the tea leaves are pointing (just opinion). Apple and Steam both have a physical presence in Luxembourg, the Brazil/Nintendo case as you mentioned “officially” were because of other reasons, but its a fascinating case and at least in my opinion it was clear that the local politicians “won” that. While it’s true you can poke holes or point to other reasons for either compliance or withdrawal in most current cases (the ones currently in the pipeline from the post 2015 change won’t finish for awhile) I’d rather look at what most businesses are doing, they have more expensive lawyers than I do and pretty sure they wouldn’t give up money without a fight.
This is also assuming that Epic doesn’t care about introducing their engine to local Universities, hosting conferences, or other typical business practices designed towards growth. The marketplace is tiny and I’m sure if it stays that way and EULA they come up with will de-facto be followed. If it grows though I wouldn’t be shocked to see a clause added to the EULA that says “except where required by local law” and also wouldn’t be shocked if they started collecting VAT for EU customers if it grows.
The whole situation like this is a total mess and there will always be tons of EULA’s on both sides and lots of fun for lawyers. As the pot of money grows, I’d place money on local politicians getting their way if they are a big enough market (like the EU or a growing market like Brazil or China). For a time or if your small no one cares but it doesn’t stay that way forever.