For me, the sense of "switch" comes not from the idea that I need to decide between playing Next ONLY while never playing PF again or rejecting ever playing next in favor of only ever playing PF but from the reality that I only need so many near-substitutes. When there's a lot of similar options, it's more likely that some of them are likely to get crowded out. Think of RPGs as Golf Clubs. If I'm a very casual golfer and my golf bag has a driver, a three-iron, a nine-iron, a sand wedge, and a putter, I'll use them for different shots at different times, so they'll all get some use. Now say that somebody gives me, like, five more drivers that are barely differentiated from each other. Even if I like all six of the drivers and I recognize the pros and cons of them, it's likely that there'll be some that just don't get much use at all, either because I like them a little less or because they're just so close to a club I'm more comfortable with that I just don't bother.
Like, I theoretically probably have time to play D&D 3.5, and I still like D&D 3.5, but I haven't played in or run a D&D 3.5 campaign any time recently because anything I'd use 3.5 for, I just use Pathfinder for instead. I essentially "switched" not because I don't like 3.5 any more or that I wouldn't be happy to play it, but Pathfinder is SUCH a near substitute that it just crowds it out. I don't think that PF and Next will be nearly as similar to each other as PF and 3.5 are, but they're likely to be close enough that they're competing for the same campaigns, and if I like one even somewhat better it might crowd out the other one entirely.
