At the time I bought the H1D I bought an adapter for the Imacon Ixpress 528C digital back which converted it to be able to be used on the V system and/or 5" x 4"with a sliding back. Cost me over £200 and I've a) not used it (because I sold my V series bodies) and b) not likely to move to 5" x 4" in the near future.
Hasselblad no longer offer this facility on their Digital backs, I suppose as they would a) rather you stick to one system and b) expect you to purchase one of each if you have 2 systems.