There are several rumors about upcoming Sonos products, and I don’t think any of them are in regards to a new amp.

In regards to a center channel, I am doubtful that Sonos would do this before they offer a center channel option with their wireless speakers.  And an amp with center channel would only be useful for home theatre setups, not for normal stereo and in ceiling speaker applications, which I would guess is a pretty big part of the market.

I don’t think eARC is a huge draw if the system can only handle 4.1 audio.  But if it’s a simple hardware upgrade, than not a big deal.

Trueplay is offered with the current amp when you connect the Sonance speakers designed to work with Sonos.