The MorphOS Development Team does not disclose which models they are going to support until they are very close to being ready to release a version of MorphOS for those models. I don't think they are going to change their ways now, so don't get your hopes up that they will announce which Mac models will be supported in the future so you can go shopping. They have always said don't buy any computer to run MorphOS on in the future, until support for that model is released, or at least confirmed that release of support for such model(s) is eminent, by the Team.
It's not like they grab a Mac out of the bin each day, and hope to get lucky with the days code. And I doubt there are a dozen models being worked on. But if there are for example 3 models being worked on, and the release order changes for some reason, no big deal. It would help their customers and userbase to know the 3.
There's no big-box returns process to fear, its hobbyist computing, anyone buying a Mac for more than its resale value is already headed for the loony bin or soup kitchen anyway.
Cheers