My hack ended up blocked against last night. Same symptoms as before:
-iMessages stop sending, and show the (!) symbol, then they failover and send as SMS through my phone using the new Yosemite feature
-if I logout, the Mac disappears from the list of devices in Messages, and, when I log back in, I can only send messages to myself (SMS is now broken, and I don't get the login notification on my other devices when the hack logs in).
-When I log back in, iMessages to third parties show as delivered, even though nothing was actually sent.
When this initially happened, I went to the Mac that I took the MLB/ROM from and logged out of it. After 3-5 days, the hack came back online. That worked for about two weeks until it was blocked again. I suspect what happened is the primary user of the workstation I cloned came back from winter holidays and started sending iMessages again, re-entering it into the database.
Today I cloned the MLB/ROM from a Mac we're using as a server and should never need to connect to iMessage (and that is about to be retired anyway). That immediately brought iMessage on the hack back online. It remains to be seen if it will get blocked again, but for now, my theory for what Apple is doing is:
-They are looking for either MLB or ROM numbers that show up in duplicate. When they find one, they block all copies of it from the database. If you reduce the number of instances down to just a single copy, on the next sweep it will reactivate just that one.
-The sweeps are not instantaneous. I estimate it takes 14 days or so to do an entire sweep.
Those two combined explain why some of you had your real Mac banned and why it doesn't work right away after you remove the cloned values from the hack. You have to wait until the next sweep reauthorizes it.
-When you do get blocked, you end up shadow blocked, where iMessages sent to yourself look right, but you can't actually send any to anyone else. This makes sense if the primary objective for blocking cloned values is to prevent SPAM. If you are running a SPAM farm, it becomes a lot harder to detect if you've been blocked if test messages come back.
Apple's general attitude toward the hackintosh community has been one of not intentionally interfering, but also not doing anything to make it easier either. I think the same is true here--they aren't going to keep iMessage working for hacks, but they are only going to do the minimum required to block SPAMmers. By basically giving you the option of using a MLB/ROM combo in only one instance, they manage to stop SPAM without preventing us from using iMessage.
It also wouldn't make sense for Apple to permablock cloned values, as that would cause problems for someone who buys a genuine used Mac whose values had been cloned/banned, creating a headache for Apple.