The M8 is a couple of mm's higher than the M6TTL or M7. I can't get my VII to work on my M8. I guess it could work with the arm forward and using a double cable release.
Regarding other lens systems, Novoflex, Kilfitt, and Komura are the obvious choices. The lenses are easy to find, usually reasonably priced, and generally give good results. The problem is finding the right adapter. There are rare and getting harder to find. Kilfitt's tend to have coating issues (and lose their rubber band trim); Komura's tend to have stiff focus because of cheaper grease. The Follow-Focus, while kinky, is a marvelous peice of engineering. I've never had one that didn't work right.
The easy fit problems:
- Novoflex Follow-Focus A (the one with the LTM thread) are 100mm from lens mount to film for lenses 300mm and longer. Since VII/VIII are 68.8mm you need about 31.2mm (but not more then) of extension. VISLEI-P is the right adapter. Follow-Focus B uses VISBA; one appears on E-bay about every 6 months. Follow-Focus C & D need modification to work.
- Kilfitt Basic lenses 150mm and longer (the ones with the LTM thread) are 93.3mm from the film. Go ahead and use OUBIO, being aware the lens have to be focused out 2mm to get to infinity. There are 2 135mm varieties. One is at 93.3mm from film. The other is 78.8mm from the film, as are the 90mm's. So these need and LTM to LBM adapter and extension of not more than 9mm. Kilfitt AN and WE lenses can be used, but really hard to find adapters are required.
- Komura lenses 200mm and longer (not the rangefinder coupled 200mm) are LTM and 76.8mm from the film. So you need a LTM to LBM adapter and not more than 7mm of extension.
There are all kinds of other lenses. Each has its own story of how to get it to work.