In my humble opinion (and the opinion of a random At&t rep I spoke to the other day), Nokia Lumia devices will get the Windows Phone 8 (aka Apollo) upgrade.
There has been much speculation as to whether or not this will happen, Personally, I have always believed they would get upgraded, and talking to an At&t store manager the other day only proved my point on why current Lumia devices will get this update.
I had a long interesting conversation with an At&t Store Rep, she says even the 1st generation WP7 phones (Samsung Focus and the rest of them) will get upgraded to WP8. This makes sense, we did see those 1st generation WP7 phones get upgraded to WP7:Mango, and if you remember, the "mango" upgrade brought with it over 500+ new features and improvements.
Also, on the business end, it does not make any sense for Nokia or At&t to spend so much money on the Lumia 900 marketing only to phase out the device before the end of the year to make way for so-called WP8 phones.
Whether or not current WP7 phones get the WP8 depends on the answer to one question
"what really is WP8?"
A. Is it a new smartphone OS, running on a totally different engine than the current WP7 OS? or
B. Is it an upgrade bringing with it new features, functionality and UI?
If the answer is A, then there is a chance (50/50) that current devices will not support it and therefore will not get this WP8. Kinda like how Symbian^3 devices like the N8s E7s will not get the full Belle FP2 due to hardware constraints.
If the answer is B, then most definitely WP8 will be on all current and 1st generation WP7 phones, take for example, the Nokia Belle update which was an upgrade of features, functionality and UI to existing Symbian Anna devices, there's was no problem there in upgrading those devices, I would think there wouldn't be a problem in upgrading Lumia devices either.
My point is there are more reasons why existing WP7 devices will get the WP8 upgrade than why not!