It seems Messages really is just a beta for Lion and will never see a production release on OS X 10.7, at least according to a bit of digging done by the French Mac-hounds over at Consomac.
The text strings within the app clearly show that they’ll be a point in time where Messages ceases to work on Lion, forcing you to upgrade to Mountain Lion to continue using it. It’s a shame Apple looks like it’s going to cut Lion users off from Messages, especially as not every Intel-Mac will be able to run Mountain Lion.
Of course it’s not for definite yet; it’s still in beta. Apple might just make it a Mac App Store purchase like it did with the first release of FaceTime before it was bundled with Lion. We’ll have to wait until Mountain Lion is released in “late summer” to find out. [Consomac via MacRumors]