The AFI situation is not immediately simple to understand - but it works simply once you slug through it:
There are two things - the camera body and the backs. The camera, originally called the Hy6 and made by Rollei, was available with three minor variations - and different names on its front - Rollei, SInar and Leaf AFI. They are basically the same.
First, the Rollei Hy6 camera and lenses are still available through DHW; the Sinar one may be available as well through Sinar. I don't believe they are availalble from Leaf. They are however essentially compatible with the Leaf AFI camera system.
AF lenses are still available from DHW - from stock. To my knowledge, they aren't making new ones, but there are still some on hand (nice pricing too).
The backs for the camera system (all 3 named versions) are two - the Sinar versions and the Leaf. The basic things, such as lenses and finders work readily on all three versions.As to film - DHW is planning to introduce a 6x6 film back for the camera (the 645 version has been avail) and that works on all versions.
Digital backs are a bit more intricate: the Leaf backs for the AFI/Hy6 family are called AFI backs, and are not generally available new (to my knowledge). There are still some backs around - in the used or almost new condition, and perhaps some in the pipeline are available. Keep in mind that there were several Leaf backs made for the camera - a 5, 6, 7, 10, and a II 7, and II 10 (which were the rotating backs). All will work. Sinar backs can also be considered.
Use of the AFI back on view cameras - the following has been stated:
"There are adapter plates for Cambo, Mamiya RZ, any 4x5 inch with Graflok, and Alpa.
Most of the view camera manufacturers made adapters for the AFi backs or they still have some stock left: Arca Swiss, ALPA, Silvestri, Cambo, Linhof, KaptureGroup and MerginX.
The only medium format camera that the Afi backs can be mounted onto are the Mamiya RZ (with a Leaf-made adapter) and AFi/ Hy6. It cannot be mounted on Hasselblad and/ or Bronica cameras."
The idea that your Leaf AFI back could just go right on an Alpa is an attractive (but expensive) path as well....
There may be another path to using the AFI/Hy6 backs via Sinar adapters, as they have their own line of adapters, and may provide more alternatives. I've no knowledge of how that works.
Finally - the relationship of a Leaf AFI back to a Rollei Hy6 (leaving the Sinar out of the discussion, but I believe it is the same as the Rollei): The Leaf AFI backs physically mount and function fine on Leaf versions of the Hy6 cameras (called Leaf AFI cameras). They will also fit and work on the Rollei Hy6 version of the camera just fine (and probably also the Sinar version, but I haven't done that). All these cameras are physically the same. The lenses are totally compatible across the entire platform, as are all accessories. The changes between the camera bodies (between the Rollei, Leaf and Sinar versions ) are very minor - two that I know of - the nameplate and the battery used in the camera. This is a minor detail, but might matter for some. There are different ways to power the back - either through just the one battery in the camera, or with a second battery on the back (for longer life).
The Rollei Hy6 (and I believe the Sinar too) typically takes a different battery in its handle than the Leaf AFI. If you are planning on using a Leaf back, the easiest and most flexible answer is to have the Hy6 use the same Leaf battery in the camera, so that you only need to take one kind of battery with you. Its not the end of the world if this is not the case - but it is better and simpler.
The Leaf AFI already was modified originally in that way. Fear not - DHW will physically modify the Rollei Hy6 version (which they will sell you) of the camera to accept the Leaf battery and at that point, the Rollei Hy6 is like a Leaf AFI. WIthout that, they integrate and work just fine, but then you would need to deal with two battery types. Not earthshattering, but worth noting.
The Leaf version of the camera (Leaf AFI) is not generally available new. So then if you are interested in the system - find a back first. If you find a Leaf back, then get a camera from DHW (modified for the Leaf type battery). Many lenses (AF too) can be gotten new from them, or in the open market second hand. Then you are good to go.
Hope this helps and sorry for the lengthy answer.
Geoff