I think you can use Sizzix with every machine including the new Ellison Big One apart from Quickutz if you have the right adapter. You will not need an adapter with the Ellison machine.
Ellison have just brought out new dies that are too big for the Sizzix, they will only fit in their new machine.
And Sizzix have just brought out borders that will only work in the Sidekick and not the main machine. But I don't know if the borders will work with any other make.
Looks like the die cut market got a whole lot more complicated!

A friend told me that Ellison and Sizzix fell out and so they will each be doing their own thing.