The 5100 was out at the tail end of 2015, I bought mine at the tail end of 2016. It was at the time, I believe, the only Processor/AVR which had all the features in place and not as was the case for a number of others, "awaiting update" or next model. It has also since I purchased it had a number of updates, 5 or 6 I believe, which included HLG update for passthrough and bass management down to 15Hz.
I do not believe the 5100 is any worse that than the others regarding bass management. It just maybe a bit more hands on to dial in. That said they all have issues of one sort or another, so swings and roundabouts. Just have look on the dedicated threads for the issues. Also it's probably the cheapest of the top tier equivalents from Arcam, Anthem, Denon, Marantz or Nad.
The 5200 may be out tail end of this year, many believed it would be last. Gene's suggestions are not unreasonable, although I think he will be waiting a long time for the redirection of the bass to the fronts and any inclusion of Auro.
For myself I think HDMI 2.1 is a given although the standard is not finalised and its only real benefit for now will be eARC, the usefulness of which is entirely in the hands of App, TV/Projector manufacturers. Also 6 overheads is highly likely instead of 4 but since we already have the XLR outs for the others it probably means losing something in the process, possibly the component outputs. I would like to see a significant update to the A5000 though.
I do not regret my purchase and am eminently happy with the results and look forward to future potential updates
. We are a ways away from 8K so I will not be losing too much sleep over 2.1 and there are other means to overcome eARC. 6 Overheads is not on my list of updates, I have yet to add the existing 4.