I saw this a few weeks ago, earlier models (under serial #300) can not be upgraded, so us early adapters are out of luck. I will continue to have to use a small 9V battery box with microdot connectors (from Church Audio) to use DPA 4060s or 4081s with the M2D2, but at least I don't have to get a set of microdot > TA-3F adapters made up, which would likely be just as bulky as the battery box (which is not much bigger than a 9V cell). I worry that the battery box might introduce some noise, though, and would be interested in any tests comparing the new M2D2 electret powering vs. external battery (Church in particular).
To address your question, the few runs I had with the M2D2 before Covid hit convinced me that it was by far the best preamp/AD I've used. Amazing results using Schoeps mics (CMC6 bodies with adapters for TA-3 inputs on the M2D2) as well as DPA4060s via the battery box, but only one run of each, into an iPhone XR.