For 1 and 4, I think there'd be structural reasons why they wouldn't be practical.
1. Slats would have to pop in and out 5 or more times a second as the blade travelled round and would be subject to all kinds of weird forces, so just making them work without breaking would have to be a massive challenge. Then I'd imagine vibration and forces imposed on the blades themselves would create more problems than the slats solved.
4. Again just my thoughts, but I'd reckon unless blades were specifically designed to do all the flexing required for feathering, flapping & dragging as well as handling normal flight loads and vibration, they wouldn't handle it.
Also it's not just the blades, but the head components, eg AS350 starflex, that come into play for that kind of system.
It wouldn't be a matter of just beefing up the blades, they'd have to be made right to handle all the fatigue caused by repetitive flexing.
My guess is that trying to cobble some kind of rigid head system from a fully articulated one would be like creating some kind of Frankenstein's monster - probably be easier and cheaper to design the whole thing from scratch as an integrated system.