Hey, @deathcross.
At this point, those are valid concerns, since if I remember correctly crypto isn't considered a form of currency, so who knows how'd they'd want to treat that. I guess we'd need to look at what they're doing with Bitcoin when someone uses it.
Ideally, though, there wouldn't be those issues. The online services and stores would just have the price in STEEM (even if it does adjust periodically), and there wouldn't be a need to worry about exchange rates. Unless I'm missing something... :)