Wouter,

That system would allow a huge amount variation in the spin luff tension. With every gust of wind the rig will move forward & the system will slacken a little.....as Greg Goodall mentioned luff tension is critical & should not vary like it would in this case.

My person preference is exactly the same as your diagram, but the pulley on the pole is simply moved to the main beam at the base of the mast. When the mast pushes forward in the gusts then you only get half of the luff tension changes.

A lot of people might think their rig doesn't move around alot.....think again....