S2 became necessary 15 years after Sonos launched. Tbat was a couple of years back. Can we start by understanding why you think S3 is due soon? 

I don't necessarily.when I purchased the S1 system I wasn't aware an update was ever likely. Now I am and so the timeframe for future updates is of relevance to me so I guess I was wondering if anyone had any thoughts before I blow 2k on new gear

S2 was released 15 years after S1. Given how slowly tech development happens in the home audio market, I doubt  S3 will happen in a shorter time than that. More to the point - what benefits are you expecting from the upgrade?

Portable speakers for one. Also want to get a new sound bar and don't want to have to run two separate systems.

Well one thought is that Sonos have promised to support fully all products for at least 5 years after sales of a product are discontinued. Their past record is to support for significantly longer than this.

Which products do you own that are not compatible with S2?

I have 4x play 1 and 2x play 5

Also integration with voice controller 

The Play1s are compatible with S2.  

The Play:5 gen 1 was discontinued from sale about 7 years ago, I think.

The split into S1 and S2 involved no longer fully supporting a few very old, discontinued products.

IMO if you defer purchase on this basis you would be crazy.

That's good to know. If it's just the play 5s that are incompatible with the s2 system then that is more manageable. 

Thanks for the advice. 

Put them up on eBay. They seems to fetch around £100, give or take.

The resale value ought naturally to depend on whether the 30% discount coupon has been claimed, but listings often aren’t clear on this point. 

Or, keep the 5 units if they are working; not much wrong with their sound, and the line in jacks gives them the versatility to do things with them like using them to make a cheap device like an Echo Dot sound like a quality speaker, in a stand alone space. Used that way, you can forget about the S1 controller once it has been used to configure the line in on the 5 unit. You could even use a stereo paired 5 in this way to make the music from the Dot sound very good.