@CCWTech Even if you can do a live migration, you would rarely want to. That means that any change to one system has to be synced to the other and there is no way to replicate the RAM between the systems. They can't both be running at the same time. So the old one has to run until everything is done, then you have downtime as you cut over. You can't do anything seamless between disparate platforms.
The problem with having systems running is that you need storage monitoring that hooks into the storage subsystem and intercepts all storage calls including cache and replicates those changes as it happens. Rarely something you'd want during a migration. It CAN add many, many hours to the process.
Of course, if going to ESXi, one assumes uptime or reliability aren't priorities. So maybe a long, slow process is okay.