This is of course assuming that ZERO merchants choose to accept XT fork coins.
That has yet to be seen. No one knows that.
Should be interesting to see what exchanges/businesses do when some accept XT and some dont (assuming that scenario plays out).
Actually this won't happen. Honestly, it isn't that hard to persuade someone to switch since they don't know all the details. It is much easier if other factors are involved such as money.
While XT will definitely have more than zero merchants, it will do exactly what theymos stated. It will cause a noticeable or even significant network split which is a horrible possibility.
This is what I was referring to:
A consensus hardfork can only go forward once it has been determined that it's nearly impossible for the Bitcoin economy to split in any significant way. Not every Bitcoin user on Earth has to agree, but enough that there won't be a noticeable split.