1. will it work, yes if you have an optical on the tv you just will miss out on the high end audio of Atmos. However you would be future proofing when you upgrade tvs. 
    
2. Apple tv would just plug into tv as a source as well as blu ray and arc would just be your output. 

Ah, thank you very much!  My next move will be to upgrade my TV, but for now, the space-saving advantage that an Arc would provide trumps the importance of Atmos audio.

Here is my TV’s panel:  https://postimg.cc/JG3GrhMQ

So, it looks like I’ll have to put the Blu Ray on ice until I get a TV with at least two HDMI inputs!

So, is that HDMI your Apple TV or something else? You can by an HDMI switch on Amazon for like $40 (depending on how many slots, 4k/8k etc..). So what you would do is just plug anything HDMI into that and then that plugs into the tv. It will sense which one you turn on and switch the input accordingly. It also includes a remote but usually you don’t have to use that. It works great.

That panel is on the back of my TV.

Great idea with the HDMI switcher!!  I’ll put that in the shopping cart, too. 

SECONDARY QUESTION:  Is the SONOS Arc able to discern signals that enter the TV from a switcher like that?  Is there an issue with delay between the audio and video signals in a case like that?

I really appreciate your answers.  I’m stunned at how many reviews/comments there are on the Arc, but none have answered my somewhat basic questions!

No worries, that’s what we are here for. Yes it should without a problem. As far as a delay. I don’t use the arc with optical but I do have a playbar with optical and have had no issues.