Looking forward to that, it's one of the things at the top of my wishlist!
For anyone looking for a workaround in the meantime, I've had some success using chained constraints and hierarchy contraptions to transform different types of movement into one another.
For example, say you want to turn translation on bone A into rotation on bone B. You can attach a third bone (C) as a child of A, and have it use an IK constraint to look at a bone you've placed somewhere stable relative to A (probably A's parent). If placed far enough away, the rotation of the IK constraint will move at a fairly constant rate as A translates around, which you can map wherever it's needed.
In my case I needed precise rotation, so I ended up going to wolfram alpha and having it calculate derivatives for me so I could figure out an anchor position that'd give me predictable x degrees degrees per y units movement. As long as the rate of change/second derivative stayed stable over a given range, it'd do the trick. I ended up putting the anchor at 3288.8, 1000 relative to the control, which gave me something like 5 degrees stable rotation for every 300 units translation... I think? It's a blur of weird equations and half-remembered calculus.
You can also go the other way, turning rotation into a sine-wave translation. Three nested calculator bones (A, B, C, each the parent of the next) can do this; set one scale axis of A to 0, use a constraint to map the rotation to B, then place C some distance from B; as the bone that controls B rotates, C will move in a sine wave pattern that you can repurpose, either with a constraint or by turning off rotation/scale inheritance and just attaching something directly.
I haven't tried it yet, but I think you could also do the same job by taking a rotating bone, attaching a child with a constraint that rotates it opposite its parent, and then track the end point like it's a steam piston... probably simpler overall!
Similar things can be done with scale by using the IK constraint (on a single bone) with compression/stretching enabled, and some really elaborate calculation can be done by chaining constraints correctly. I learned a lot of this while experimenting with a fake-3D rig for a foot that could yaw and pitch independently, which required some pretty strange convolutions to work!
Lot of gotchas and limitations of doing things like this, but all three of the basic transformation types (translate, rotate, scale) can be manipulated like this if you're creative about it and don't mind your constraint list getting intimidatingly long!
