Diversions during short to medium range operations in europe are not that big a deal, it is quite a different thing on longhauf flights. In a previous company we had it only for those, but never for our much bigger short haul european operation. Probably a similar thought exercise at ryanair. Of course, additionally you need a means of direct voice communications with them. Which in europe means satcom as there is no ground based phone system for planes. And all of a sudden it becomes very expensive, as planes have to equipped with it, it requires maintenance and of course, if one of the bigger antenna solutions is used, it has a drag penalty on every flight.