I finally got my 4520 and absolutely love it. The upgraded Audyessey calibration has really improved room sonics, especially for the 2 subs. I really doubt though that MDA/Atmos will be upgradeable options via downloads. But I don't expect any BR releases with those formats for at least 2 to 3 years at soonest, and even then it will likely be very limited initially. So in my projection I don't see these interesting formats having much impact for another 3-4 years and by then with other audio advancements I would be willing to upgrade from the 4520.
Yes you are probably right
ah so, the never ending upgrade-itis, I understand, glad to hear the 4520 exceeded your expectations, I'm looking forward to mine, and trying all DSX vs PLIiZ vs DTS Neo-X in my 11.x set-up