Aha.
That's exactly what I was waiting for. So long as useful accessories are available across models, older models retain value with these accessories. Releasing an upgrade version in the same year is very rare--at least, I had never heard of it happening before. This definitely helps first gen buyers, both the early adopters and anyone considering the MS inventory dump. It would've been a very bad business decision to delay a battery cover with all the rumors and whatnot for a new version of SPro.
Choice is full-price Pro 2 or, I assume, a much cheaper keyboard battery compatible with both 1&2. (@demandarin: An extra battery in the keyboard is definitely not going to be cheaper than the existing Type keyboard. That's crazy talk.
)
I must wonder, however, how the Pro 2 price will be compared to a cut-price Pro 1+battery keyboard.