I agree, backward compatibility will be a very good thing.
I don't understand how there was ever going to be a beta if it was impossible to downgrade back to the original firmware if there was a problem. But the decision to add backward compatibility was just made yesterday. The beta was promised numerous times over several months so they must've been pretty sure that it was possible.
If, at the time of all the different beta teases, Netduma wasn't looking to add backward compatibility functionality, they would've stated that in at least one of the beta announcements right? Something along the lines of, "Beta is soon! Warning: If you participate in the DumaOs beta you will not be able to downgrade back to the original firmware in the event of a problem" would be expected.
If not in one of the beta teasers, surely they would've said it one of the times they had to announce the delay of the beta. I remember an announcement/comment about the beta being delayed that said something about it being a "real" beta which could include some bugs, it wasn't a beta like COD which is basically just a trial version of the finished game. If that's the case, I don't see how they could've been so serious about a community wide beta if there wasn't any real backup plan if there were catastrophic problems. Obviously that beta never happened, but it was hinted at long enough and enough times that it's fair to assume that Netduma wouldn't keep promising something that was that risky.
If the decision to add backward compatibility was made yesterday, how could they have hinted @ an open beta in Fen 2017 without their legal team voicing their concerns from that time up until yesterday? Especially when the beta would've been much less stable than a full release. It defies logic.