As there is not currently any plans to bring this game to a newer version of Total War, I have included a link to a Medieval 2 Kingdoms mod which is a very similar timeframe and area to this mod.
Invasio Barbarovm II MODdb.com LINK
Invasio Barbarorvm 2: Conqvestvs Britanniae III download page on MODdb.com LINK
Map consists of Britain, Ireland, N. France and the lower Scandinavian areas.
Set in 452 AD and Rome has withdrawn from Britanniae bringing forth various Briton or Romano Briton factions, this is also encouraging the Saxons, Angles and Jutes to visit Britanniae.