I have just updated four LIFX lamps to the new firmware [2.75]: 4 x LIFX + A19 and 1 x LIFX Downlight.
Running LIFX Controller plugin version 5.07 [from the {Plugin Store], all lamps with the new firmware were finally detected.
So it seems there might need to be a couple of restarts of the plugin before the new lamps are detected. Restart the plugin after the first successful discovery (for other lamps) has completed - this may be the second discovery attempt (depends on how many lamps you have). It may also need a subsequent plugin restart.
So from what I am seeing and have tested, the new firmware works OK with the plugin but may take a couple of plugin restarts to make that happen.