Personally I have a 2014 5K iMac i7 with a fusion drive. I have a Fedora VM on it I run occasionally. I run it using Virtualbox which is a free virtualization system. I've allocated 4 GB of memory and it's very performant. It's a great way to try out virtualization at home and you can run Virtualbox on Linux, OSX or Windows as the host OS.
Somehow, I thought there was this magical hypervisor that would give all to one OS that I could use and then, out of nowhere, I could switch to another OS in a way that first one would go to sleep and its memory put on hard drive and the other one would wake up its memory from hard drive and show up. I wouldn't need them running concurrently, but I would like to have them switch fast.
In a way I would like to consolidate three machines into one without having to run three machines or wait for shutdown/boot sequences (with multi boot).
Bonus would be to share disks (non boot ones) and copy and paste. That would be really great.