can I get ceiling speakers for my system?

You can add ceiling speakers, but they would not be part of your current room.  They would be a separate room for music only (grouping with your current room would cause an echo for TV sources).

ok thanks. I’m thinking out loud here, if they where attached to the TV firstly could I use delay to stop the echo? no! because the gen would also have the delay. 2. would there be any benefit swapping the eras for ceiling surrounds/Atmos. I’m not bothered in other rooms I have alexa to do this.

is it just the lack of computing power that stops me having 5.1.2 or can it do 7.1  with a work around?

There is no benefit to TV sound if you group another room with the Home Theater setup.  Any grouped room, aside from the delay, will play all channels - L/C/R fronts, L/R surrounds, and L/R Atmos - as a stereo downmix.  This will wreak havoc with the mix; defeating any directional cues.  More speakers doesn’t mean the sound will be better.  

As to swapping the 100s for ceiling speakers, the ceiling speakers would not be Atmos capable.  They would be receiving surround channels only. 

Currently the Arc, Beam 2 and Arc Ultra can do 5.2.4 (L/C/R fronts, 2 surrounds, 2 Subs, 2 Atmos in front and 2 rear Atmos w/ Era 300 surrounds).  However, the x.y.z designation is passe.  Given that Atmos is a positional codec, individual channels really mean nothing when comparing room to room configurations.  

The only way to get Atmos from rear speaker would be to replace the Era 100’s with Era 300’s. In my opinion this would be overkill with the Beam (Gen 2) you are using for fronts though.

Sonos does not do separate height or side speakers (so in ceilings will never give you Atmos), because Sonos isn’t about “packing rooms full of speakers”. If you want the full Atmos experience with Sonos go for the Arc Ultra and combine that with Era 300’s.

I have what is probably the std layout with the era 100s either side of the settee at about ear height (room dictates this) so even in Atmos theres no mid way or back height in the sound so I was thinking that ceiling speakers would bridge this gap. I’m re doing the room from about Feb next year so I can lift the 100s by about 50mm before ‘she’ notices.

AH! should have said Beam Gen 2 not just Gen 2, sorry guys didn't realise. so does this make a difference?

The Beam Gen 2 has virtual Atmos drivers, the Arc and Arc Ultra have physical Atmos drivers.  So the Arc models are going to give better Atmos effects.

She is not going to let me go that far as to replace the system but I could go as far as ceiling speakers but hey I will settle with what Ive got unless I could utilise Alexa as a height speaker?

Alexa? Nope, you can only use Sonos devices, and as said not all of them will give you full use of what you have.

You could replace the Eras with a Sonos Amp, bonded to your Beam, and ceiling speakers. Lot of expense and hole cutting for what would be non-Atmos and likely less pleasing sound.

Instead of replacing, consider moving the Beam and 100s to another room and adding an Arc Ultra and Era-300s. No other room, consider kids, grandkids, parents (old ears will love the Beam) and rehome them.