I'm not sure whether Beryl (or probably compiz-fusion in the somewhat near future) should be ditched. I guess it makes sense to keep it due to popular demand.
But a foolproof way of installing and configuring Metisse, as an option, would be great. I tried Metisse on the Mandriva One 2007.0 CD (I think it was created as a demonstration for Metisse), and it has interesting usability features.
But integrating Metisse in a foolproof way might prove hard. Metisse is much more experimental, and there might be concerns about the future of the project. It is created (and maintained?) by two UI researchers, and integrated in Mandriva only as far as linux distros go (unless I'm mistaken).
So, my advice to the Linux Mint team:
1. try it out (with the Mandriva One CD, for instance);
2. if you're considering getting it in Linux Mint, talk with the Mandriva people for some tips.