HTC’s confirmed to Engadget that the “cupcake” OS Update will should be available to the T-Mobile G1 some time in the future.
https://gizmodo.com/cupcake-roadmap-hints-at-whatll-be-in-the-next-android-5113029
No specification on when the over-the-air update will hit, though. [Engadget]
Chris from Engadget just told us that it’s still up to T-Mobile and Google whether or not the update will hit, but HTC believes it will—but they can’t mandate it.