Some people think it's not worth the trouble of learning Emacs, at least not while they're tasting Lisp. If more people had a positive experience while using Lisp, maybe more people would use it. When weighing the costs and benefits of using Lisp, I've never heard anyone say the benefit wasn't great, just that the cost was too high. Costs could include anything from lacking libraries, having to look for libraries, having to use Emacs, no standard implementation, etc. Some people might prefer Eclipse, who knows.
I think they made enough good points that my new policy will be to recommend Emacs, but mention Cusp as an alternative.
Probably very low. Until the entire environment gets easier, I think most people that successfully learn Lisp will be the most dedicated to it, and if they're that dedicated then they'll want a more powerful editor.
I think they made enough good points that my new policy will be to recommend Emacs, but mention Cusp as an alternative.