It's weird that you've said so much and yet you're apparently not aware of the upcoming 2600+.
I do wonder how compatible it will be with expansion chips (like the DPC in Pitfall 2). I assume they have an internal list of recognized games, but I wonder what happens if someone wires up their own homebrew game with one of those chips and plugs it in?
But you're right, I should have mentioned it because it's a good idea to do and a legit product, I just had it purged from memory because I wasn't interested in it.
As you suggest, one way around that is to fingerprint the cartridge and then to load a binary into the emulator from internal memory (if they're using Stella then the emulator is capable of emulating the processors on those chips) but I don't believe that is an option provided by the 2600+. And if it was, it's a very limiting option for the end user because new homebrew games wouldn't work.
I think we need to be reasonable about how much magic we really expect them to put into this thing, since running Atari and Activision cartridges, like the 2600 (and 7800!) of old, is what most people would expect the machine to do. On the other hand... if they make the machine easily hackable, that might be pretty great, and earn this version of Atari a little respect.
If the market for this product is people who only want to play the older ROMs on a HDTV then I'm sure the 2600+ is a fine product.
Maybe I'm projecting from myself, but if I'm that kind of enthusiast that held on and wants to play their actual cartridges, I'd expect compatibility with any cartridges I might still buy in the future.
(Then again, both the RetroN and Polymega seem to do well enough, so what do I know, apart from not liking the idea of these systems as half-baked in-between solutions.)
It seems to me that compatibility with any cartridge would require a recreation of the actual VCS hardware. That sounds expensive to me and is probably why Atari haven't gone down this route. But as you say, that leads to a half-baked solution.
The other option is an emulator that can communicate with the cartridge in real time - but that doesn't exist and I doubt Atari have gone to the trouble of making one (we're all assuming they're using Stella at this point, but I don't think that's been confirmed).