I do not believe EASA have any immediate plans to regulate state aircraft (in fact, I don't think they have any long term plans to regulate State Aircraft either). The ANO has been amended to allow UK registered non-EASA aircraft to be flown by a pilot holding a Part-FCL (EASA), Licence. Article 50 of the ANO should give you all of the information you need.
This is a bit of an old presentation but it should explain things!