Dude, there's no betrayal by Yihi, there's just a single source rumor, and could likely be from an Evolv fanatic stirring the pot. Everything else points to the opposite, that there will be in fact continued support of the SX-350J V1.
If they can take the time to update the firmware on their least expensive board (the 130H) two months after release and after very very strong sales (i.e. no real market need for updating it), it leads me to believe they'll continue to support the M-Class, especially since they're still only going to be selling the SX-350J V1 to modders, who expect longer term support. They are not releasing the SX-350J V2 to modders at all, that's exclusive to the ML.
I suspect that the delays on final, non-beta firmware for the SXM is them simply working out all the kinks as they develop the SXML, and that they'll have a final SXM update about the same time the ML releases, and it'll be very similar, sans a few extra features that the ML will support.