Bonz, do you intend to stay with Sonos serving up your music? What is your budget?
If you intend to replace the Sonos, you will need to find a new means of serving up music to be transmitted to the new wireless speakers..
A Sonos Connect can be used to deliver music wirelessly to active/powered speakers, or to feed a separate amp and speakers. There will need to be wires from the Connect to the speakers or amp though.
Alternatively, a Sonos Connect Amp can power most small/medium sized passive speakers. Still will need wires to the speakers.
The Kef X300a or X300a Wireless will provide a big step up from the Play 3's and old Play 5's. The new Play 5's are an unknown at this point in time, but I'm doubtful they'll match the X300a in sound quality. The Kef X300a will still need something to feed them with music though, if thinking wireless. The Wireless version uses Bluetooth and Airplay.
If your budget will stretch to it and if you require a total lack of wires to the speakers (apart from the power chords), then look at the Dynaudio XEO 4. These are much bigger in size, but will take sound quality into a completely different league. With the required XEO Hub, they will set you back around £1550 'ish (best price shopping around), plus you'll need to budget for proper stands. I think the dedicated XEO stands cost round about £210? XEO 4 + Hub + stands + Sonos Connect = approx. £2000.
Personally, I'd forget the Zeppelin, although B&W do have some other, better sounding wireless speakers in their range. Sound quality will still be in a lower league though.
z