Here is why I don't think current devices (even the 900) won't get Apollo....
Both Microsoft and Nokia knew, before the "huge marketing" they have been claiming will come with the Lumia 900, that NO device would get Apollo. So why release the Lumia 900 only to abandon it 6 months later...? One word: hype.
Think about it. If they can get the Lumia to sell well, developers will come. The Lumia was meant to be a "here, look at what Microsoft is doing with a beautiful device" type of device to spark both consumer AND developer interest. This why Micorosft is only saying "all apps you develop for Windows Phone NOW will work later...". They carefully and purposefully worded that for DEVELOPERS because lets face it...developers WILL buy a different device when Apollo is released when current devices will be abandoned. They released the Lumia for APPS and HYPE as a precursor for their "strong push" with Apollo, so that developers will get behind a beautiful device, that has hype and marketing (if it indeed is selling well), and has a PROMISE of having backwards comparability for the APPS that are written for that beautiful device....
Microsoft knows they lost this round, and they know they will p'off a lot of their "cult" (being us, people who know about forms because lets face it....those are the majority of windows phone users). That's why they are starting over. Carriers (even Verizon) have said they will support Windows Phone 8, but do you think a carrier (especially Verizon) meant that in reference to current devices (their one device in Verizon's case)? No. They meant "hey, when you guys get Android-like high end specs (WITHOUT android), and put a beautiful OS like this (Windows Phone 8) on it, this could definitely compete with iPhone and Android (which they said they want so that competition will balance out more) and make us good money!".
I see Microsoft paying attention to the most important players here and the ones standing in the way of success: developers and carriers. They HAVE to get them on board first. In the scenario I described, carriers would be happy to rake in incoming new customers with the high end devices (to sway the Android following), and developers would know that apps they develop for WP7 will work later just fine (an issue Android is having with its fragmentation issues). In the end, someone has to lose, and it CANNOT be carriers. Unfortunately it will have to be us (and keep in mind that that's an EXTREMELY small number).
That said, I think Microsoft will be INSANE if they don't offer a similar program to their "Smoked by Windows Phone" campaign where people can trade in their current device for a Windows Phone. To "make things right" Microsoft BETTER do this (if I am right) because the average smartphone buyer won't pay 600 something dollars for Windows Phone 8 because they won't know why it's so valuable enough to pay 600 bucks when they JUST purchased a Lumia 900 on a contract....
Ironically, as others have stated in reference to the Smartphone Beta Test commercials, every Windows Phone user would be a beta tester lol...even for the device they are promoting. Why Microsoft would push this "beta test" for this long, knowing it was failing and waste people's money is beyond me though. They may have had high hopes that it would succeed, but after a year of no success and knowing the next update(s) wouldn't bring dramatic changes that many people cried for that were missing, they could have collected the complaints and "beta results" and had Windows Phone 8 AND the nicer devices out by now....