Stone fireplace wall effects on acoustics?

Very negative will kill imaging and bass.Good luck though!!

Try your preferred layout and see what it sounds like. Given you want to limit first reflections I doubt the fireplace will be any worse than a regular wall. It will probably sound better than a regular untreated wall.

I'll echo Pauly and add- the suck out problem, as I know it, typically arises when people put their speakers to either side of the FP, which may look grand but as all of you are aware, has to be dealt with. Hard to predict in the abstract how it would affect sound on a side wall and apart from the hole (FP), you might wonder what the rock sounds like (as opposed to sheetrock or whatever lines your interior walls). 
Agree, set up and optimize- I did a move several years ago, and even with the same system, it took me time to dial it in.
I don't like aftermarket acoustic treatment generally, but use unobtrusive bass traps and window treatment, not uncommon...
Even if somebody digitally mapped your room it's not the last word, it will be ears in my estimation. If you need help, talk to several somebodies who have done rooms. You can learn from their mistakes. I'd pause before I spend a fortune on room treatment. Some of this may be in positioning of equipment and sweet spot. 
This is just the beginning....
and good luck!

Not trash, no. Random bumps like that can be viewed as a sort of diffuser. Better than a flat wall. There's no such thing as a perfect room, especially not in a case like yours where it has to balance with sweet spot listening, background in the kitchen, etc.  

Everyone wants the one and done solution, when really the only way to know for sure is try it and see. If you care about imaging, by far the most important factor there is symmetry. Set them up equidistant and symmetrical and if you like the imaging then you are done. Even here though, once again it is a balance. Toed in for the best imaging when sitting for serious listening might have to balance with how it sounds from the living room other times. Again no way to know other than try and see.  

The other thing about location, speaker distance from walls affects tone and frequency response. Don't be distracted by the fireplace, there's always more than one thing going on. And, guess what? The only way to find out is set it up, listen, and see. 

Only after trying and finding you hear some flaw, only then we work on the flaw. Until then it is all internet blah blah blah. Which we have in abundance! lol!