I actually started to do it once, after I read a book that utilized it to really good effect. In that book the FMC was written in 1P and the MMC in 3P. It was all past tense.
When I converted one chapter of my story to this plan, it turned out fine. The people who read it didn't have any trouble switching 1P/3P with the POVs, which were already a switch for them anyway.
I really liked getting deeper in my FMC's POV because she's unreliable, and having that 3P for the MMC for the same reason. (He doesn't really know what's going on with the FMC except what he sees on the outside and what he's intuiting, so that bit of extra POV distance helped her stay more mysterious, if that makes sense). But, dang, it took a lot more brainwork for me to switch while writing. I kept finding myself slipping into the wrong POV and have to go back and find all the wrong bits. I was @_@ after just a few chapters and I gave up the experiment, even though I still think it would be a good way of writing that particular story.
As for your mafia story, if you already have an established readership, maybe consider what our "brand" expectation might be from your readers? Otherwise, it's a new story so you really can do whatever you want with it. A lot of contemp is 1P (but not all, by any means), Regency is mostly 3P, and some readers are so particular about POV they won't read one or the other, so you can't please everybody.
You could also try doing a "look inside" for several top-selling mafia romances (or whatever's hot in KU) and see if there's a pattern if you're writing toward publication. Or just do what feels right. That's probably the best way to tap into your best storytelling instincts.
