You might want to take this one with a heavy garnish of pinched salt, but a post on the PTCRB suggests that the firmware update required to run Ice Cream Sandwich has been certified for the Xperia Play.
As Xperia Gamer has pointed out, the firmware build version, 4.1.B.0.431, is the same one that's been rolled out for the Xperia Arc, one of the phones that will be getting updated to ICS in the not too distant future.
Of course, a firmware update doesn't necessarily mean anything, and there could be plenty of explanations for why it's made an appearance. A lot of work had already gone into the ICS update for Xperia Play, and it's entirely possible that this is just a remnant left in the system after it got cancelled.
It seems unlikely that Sony has changed its mind so soon after announcing that the Play wouldn't be receiving the upgrade to Android 4.0, but we all love a mystery, so it might be worth keeping an eye on your Xperia Play in the coming days to see if the firmware does actually turn up.