I feel like that special guy (sorry ladies women's boxing is a mess where some of the best fighters like Ann Wolf could hardly make a living) will come along and leave his mark in both sports. Sadly it doesn't take much or mean much to get hold of an alphabet soup belt in boxing. But I think (hope) we may see someone who can do it and be very competitive in MMA. The only guy I can think of who did well in both sports was Kimbo Slice but he wasn't about to set the world on fire.
If I had to guess, I think if we were to see a breakout star who could cross compete, it would honestly be someone from Russia or one of the former Soviet States. Not only do they have many quality boxers but both Sambo and Kyokushkin Karate are very popular over there, which provides some great cross training opportunities. It would be interesting to see how it would work out though, cause compared to MMA boxing is very much a finesse sport. It's unfortunate that women's boxing is in such a state though. Currently in MMA, whether you look at The UFC, Invicta, or elsewhere, the woman's field is very thin in quality competition at the moment. Now is the perfect time for a strong boxer to make her mark in MMA, much like Rhousy is doing, before the field gets too tight. They'll have a much harder time down the road as the women's segment matures.