I think Pentax medium format will increase in value for a few reasons.
- good old supply and demand. people are certainly buying the gear, but it is no longer being manufactured. the supply from those who go digital and also choose to sell film cameras is small compared to what a manufacturer contributes.
- Best compatibility in medium format. 645D can use all the Pentax optics, including outer bayonet mount lenses which attach on the outside of adapter 645.
- People who buy Pentax lenses/adapters with the 645D in mind are likely to buy film bodies and backs as well.
That's my take on Pentax gear. I use a 67II and also have a 645n. They are really outstanding cameras! The 645N will accept Pentax 67 lenses with the adapter we are talking about--be advised it will accept Hasselblad CF lenses with an adapter available on eBay. With CF series you can lock the depth of preview and use stop-down metering--there are probably other Hasselblad lenses that work.
Because of the digital daze, and a temporary price crash, I was able to get some really outstanding gear and low prices. But when people buy up the cameras, they will also buy up every accessory that goes with them, including lenses, bellows units, cases, adapters, focus screens, and so forth.
In once sentence, a big supply will change to scarcity. The 645D looks like a nice rig--too expensive for me though...