Holly & Phil apparently have a pact that they will leave together. Holly is unambitious and is known as Little Miss No for all the new projects she turns down, and Phil is happy working with her so I think they'll be there for a while yet unless some sort of scandal crops up.
Eamonn and Ruth are sidelined by the powers that be (I assume there's no love lost between Eamonn and Martin Frizzell) but are apparently far more popular with the This Morning 'family' than Holly & Phil. I spoke to someone recently who alleges Holly and Phil waltz in, present the show and disappear straight after the production meeting whereas Eamonn & Ruth have a closer relationship with the team behind the scenes. I can believe that, based on what we see on screen.
It'd be a huge mistake on Eamonn and Ruth's part to do a show that competes against either show and 5 have learnt that the hard way with Terry and Gabby, Trisha Goddard and Live from Studio Five that competing against a similar show never works. Not to mention Do the Right Thing failed miserably and that was in primetime.
With all due respect, Live From Studio Five was rubbish, Terry and Gaby was 15 years ago and I've not even heard of Do The Right Thing so it can't have been well publicised.
The closest comparison to make is Richard & Judy leaving ITV for Channel 4, which worked on the strength of their on screen chemistry and a solid format. It would be a risk for Eamonn & Ruth but Channel 5 has stepped things up a gear in terms of quality. I'm also confident they'd also take some of the TM family with them, they're that well liked.