Ryanair don't make that information public, also things can change massively over weeks in the business.
I've tried to find the link but to no avail. They did release their top ten routes a while ago and Manchester - Dublin was definitely in there.
As you say though, these routes will change all the time but look at all major airports/metropolis regions that Ryanair operates into - not one (apart from MAN!) has only one route. Cost wise it isn't worth just having one route...unless...it's one of your star performers.
Remember the route is only a few hundred miles long therefore costs won't be too high plus their benefits of economies of scale in DUB...
Just a thought but if anyone can find that link it would be interesting!