Actually, now that I've read the press release I'm pretty sure this isn't a new device. From what I can tell the XO-4 Touch is simply another name for the XO-1.75 Touch which was announced a couple weeks back.
Today's news is vague enough that I can't really say that these 2 XO models are different, so until I get some photos I'm going to assume that all that happened today was that OLPC changed the name. That is enough of a good idea that it makes more sense than having 2 different touchscreen equipped XO laptops.
But it also raises the point why OLPC couldn't have figured out that XO-4 was a better name in the first place. That's not a good sign that they have their wits about them when it comes to basic marketing.
Update: I now have some details about the XO-4. It turns out it has a different and newer Marvell CPU. The XO-4 has generally the same specs as the XO-1.75 (listed here) but it's also going to add an HDMI out port at the cost of one of the 3 USB ports. So it is a slightly different model.