I think a Rhys/Gwen/Jack/Ianto foursome is actually more likely than a Ianto/Jack/John....why? Because it doesn't seem like Ianto *likes* John, and he doesn't even trust him as far as he can throw him. Maybe for one kinky night, but....yeah, I actually don't see it.

But the foursome I can see happening sort of as a comfort thing, at least short term. I think everybody needs everybody right now.