you cant show only one card anymore, maybe thats just in tournys but its a new rule.
It's not a new rule, and only applies to winning a hand. To win any portion of a pot, a player must show all of his cards. So you can't show one card to win, even if you just playing one card. But this is not new.
As far as folding goes, if it is down to just two players and one bets, the other decides to fold, he can show none, one/some (depending on game), or all of his down cards.
While not every site will give you everything, I would like to see the major sites incorporate these extras into their software. Take
pokerstars for example, while I very rarely show my cards, but if you're facing a big bet you don't call, they don't even give you the option of showing your cards at all (unless there is a setting I'm missing somewhere), much less just showing one. And if you bet out and your opponent folds, you obv win the and by attrition and don't have to show anything, but your only choice is muck or show both. Showing one would be a nice option.
As far as rabbit hunting goes, not sure I like it or not, tbh. I think it could produce a lot more results oriented, "Gee, gosh, see I knew I should have called" type play. That said, if I had to request it, I'd say keep it totally out of tournament play altogether. It doesn't belong there. If it was going to be incorporated, I'd have it put in ring games only, and only available when you fold to a turn or river bet. Maybe even take it a little further and say that you can rabbit hunt only if you fold to an all in turn or river bet. IDK, I still think it could drive even more result oriented or tilt play, but I can see it's merits as well if you are simply using it for interest purposes on what you think are marginal decisions and not for guiding you to bad future calls because you "know it's going to happen". But regardless, only in ring, not in tourney.