1. Inadvertant spins
2. Structural failure
3. Engine failure above mountainous terrain or dense forest
a CB strong enough to cause structural failure would also suck you up to 35,000 feet or more. If a Cirrus wing fails at around 9G, it could turn the chute into hankies
Within one CB, you get multiple columns of air, each going up and down. Each can be a few miles across, so you go up one minute and down the next. The structural failure risk is not from the vertical speed itself; it's from the vertical acceleration resulting from flying too fast through the boundaries between these.
I am sure it would take a lot to break the wings off a Cirrus, or a TB20 for that matter. Probably flying into a nasty CB at close to Vne. But once a wing breaks off, the thing is just going to plummet; around 10,000fpm (100kt vertical speed) according to some NTSB reports. No CB will suck a 1000kg+ lump upwards, IMHO. The chute should work.
Re Permit planes, they can't go IFR and that severely limits mission capability. One can do a lot going "ostensibly VFR" especially if bending every rule enroute but you still end up scrapping some 90% of preplanned flights because you would never get back down.
While it is very possible that VFR-only 140kt composite planes costing under £70k will (over the next 20 years) suck the £250k+ European IFR aircraft market dry, there will always be a demand for planes that can carry 3-4 people and stuff across Europe. The flow of new models will be assured by the US market which has a large IFR contingent (accessible IR, etc).