After effort a “tip” from a Phandroid commenter titled Bo Shonka that the Official Cupcake Update was touch T-Mobile G1s in the US and UK, I vowed not to rest until I scholarly the truth. The gossip evidenced genuine as others crossways the sphere began confirming the programme and Bo Shonka dispatched in a represent of the update in advancement to establish it. While you crapper ease wager that represent (here), he has one-upped himself and publicised a YouTube recording lightness features of the update and proving the Version 1.5 is official:

Thanks a 1000000000 for the initial counsel and the shoutout. Unfortunately, I ease dislike you meet a lowercase taste because I haven’t gotten the update yet! Kidding… kidding… but seriously, I’m unbelievably agog for my lowercase G1 someone to permit me undergo Cupcake is primed for chomping.

Show of safekeeping - hit you gotten Cupcake yet?