Is it possible to wall mount the new playbase?

Is it possible? Sure, anything is possible. Is it advisable? Hell, no (excuse the profanity...but it's that important). How would you mount it behind the TV? Would is be facing down, so the speakers are all pointed at the shelf it's sitting on? Frankly, any obstruction of the speakers would make the sound be less than desirable, and you'd be regretting the expense.

The Playbar and Playbase by Sonos are designed to be in open space, not behind anything. I don't have a good mental visualization of the space you're asking about, but if I was serious about going with a Sonos system (and I do happen to love the no-wires surround, particularly) I'd be thinking about getting one of those Flexson surface mounts and a Playbar, rather than a Playbase, and have it mounted below or above the TV attached to the wall/shelf in some secure manner.

Is your tv on the tv shelf? How big is that? By saying that your GF bought the tv shelf, are you saying that getting a decent size shelf will be vetoed?

Change the shelf. Or change the GF. Don't wall mount the Playbase

The you guys for your help!

The width of the TV shelf is only 28 cm, so fitting a playbase wont look good at all. The playbar would fit perfectly wall mounted or below the TV but without any experience of any of them, the playbase to me just look better :)

Another question:
Does the playbar actually add any sound quality to the play 5 I already own? Or is it better to have 1 separate system for the TV and another for music? I live in an open floor plan and think the play 5 does perfectly good on its own. My livingroom however is over 60 sqm^2 (645 fqft).

Well, the Playbar/Playbase units are designed to be used with a TV via the optical output on the TV, and consequently have no audio delay, so that lip-sync isn't an issue. If you were to connect the TV in some manner to the Play:5's analog input on the back, there would be a ~70ms delay, which may or may not cause you to notice a significant issue with lip-sync.

I have both a Playbar and several other Sonos speakers. I tend to not use the Playbar as a music player most of the time, but that's probably more of a function of the room that it exists in, as the sound is outstanding.

If music is the top priority and you think a P:5 sounds great (which it does) then get a second P:5 and use the two as a stereo pair. If you want better TV sound than the internal speakers but have no ambitions for surround sound, get a smaller, cheaper, non-Sonos soundbase or soundbar. Depends what your aims and priorities are.

I don't have a play5, so can't compare too much. However, I do have a playbar with 2 P3s as surround and absolutely love it. That said, I think I would love it just as much with 2 P1s for surround. If you watch tv and music a lot, I would try the playbar alone and move the play5 to the bedroom (maybe make your GF happy?), and look into getting 2 P1s if you think surround is worth it.

If you really like that, then dump the GF and used the money saved to get the SUB too. (kidding!)

I don't own a Play 5, and I've only listened to one in the terrible environment of a Best Buy. My belief is that the Playbase/bar will present a wider sound due to the array of speakers, but it would lack in some other areas compared to the Play 5.

The Playbar can be wall mounted. Sonos actually makes a bracket to wall mount it.

The Playbase is not designed to be wall mounted.