Paul Thurrott has written an article on WinSupersite where he summarizes and also ads a few details on upcoming Windows Phone updates.
I wont repeat everything we have read before, but a few new bits drew my attention.
He notes that Tango, probably to be called Windows Phone 7.5.1, is aimed at low-end devices with low memory, and will have certain resource-intensive background tasks disabled. They will however be distinct from Mango devices, in that these handsets will not have access to the full range of apps in Marketplace. Apps will be certified separately from them, and developers can choose to have their apps tested from low memory Tango devices or not. Paul notes for example that Angry Birds will be available on Tango devices but Plants vs Zombies not. He also said developers will get access to Tango soon to test their apps in low memory situations and that the OS is expected to be unveiled at MWC 2012.
In conclusion Tango devices will be similar to Mango devices, they will not be the same, will not have the same range of experiences and will probably get updates separately.
In the article Paul does not address the issue of whether Mango devices will be upgraded to Windows Phone 8, but certainly one can assume Tango devices will not.
While the Microsoft solution of having both a low-end and high end OS is more clear cut and likely to cause less confusion than having a range of devices with varying abilities like on Android, it is certainly safe to say the situation is going to become more confusing in the future, and consumers will need to be very careful when selecting their devices to enable greatest access to Marketplace at the lowest prices.
Read more at the WinSupersite here.