Ah, well, on the M1G itself, sure, I don't see why they wouldn't support a V4 version of firmware on the M1 panel; just logging into my Elk account, I see they still have 4.6.8 posted (although it is listed as a Legacy version); current being 5.3.10 (released 7/11/2016).
I've seen nothing to indicate that V4 wouldn't work there. I've been on multiple calls with Alarm Relay technicians during the setup process and have never been asked to confirm firmware version(s) to date. They simply step through the setup/configuration process, and then ask you if you'd like to test the reporting by arming your system, violating a zone and having the alarm report to them.
How are you looking to have monitoring setup? Internet, cellular, POTS?