It has been confirmed that any Sonos speakers that are compatible with S2 and can be used as surrounds will work with the Arc.  That includes Play:1s and Play;3s.  Your Sub can also be used.

Yes. This was discussed in the Arc announcement thread and Sonos clarified that it will work with any speaker pair, same as the playbar.

Thanks for jumping in! Both John and melvimbe are correct. Please feel free to share with others if you see the question come up.

So just to clarify ….

I have Playbar, current sub. (not the new release, i have bout it in 2017 new), and 2x Play 3’s for my surround.

I will be able to JUST buy ARC and use my previous components correct? still pushing Atmos.

OMG … i think i just found 

https://support.sonos.com/s/article/4786?language=en_US

That is sooo confusing … i see why people are freaking out.

Yes those speakers will work with the Arc. I think whether you get Atmos depends on the TV (and of course the source), but the Sonos speakers are up to it.