If they shutdown Play Music, it might look similar to the end of Google Reader in 2013. They might be looking to get people off the service until they announce it.
You can buy dozens of different shampoo brands (because you like the bottle of this or the smell of that) and in the end your money will end up flowing to the same company; but $deity forbid that I could get two same-but-different services from the same company if they can avoid it. I mean, I get the operational savings etc etc, but if they are both profitable, why go through the pain and suffering of killing one?
Then you turn to another niche (like IM) and it's the opposite attitude.
Google's commercial strategies are pretty nonsensical.
They’ve semi-threatened it will be killed off sooner or later anyway, so I wouldn’t be surprised.