I have kindly been allowed to see a draft of Dan Mersey's upcoming dark age rules that Osprey will be publishing. I am very impressed with what I have read and am looking forward to trying them out as soon as I have a couple of other projects put to bed.
Overall impression is a game in the same spirit as Impetus, but with a nicely thought out set of mechanisms to reflect the difficulties and character of warfare in post-roman Britain. As I had planned to re-work my armies for Impetus anyway, this should dovetail nicely and still allow those diorama bases. Measurements are in base widths which helps! I think I'll go for the Impetus standard of 120mm bases as these allow about 12 infantry or 4-5 cavalry.