Question 1: I think concentration is a good idea. I'm not currently convinced that it adequately addressed problems with D&D's magic system as I see them.
Question 2: I agree that such a feat should not exist.
Question 3:
That's how I understood it as well, but I do think the wording was a little convoluted and unclear.
I think it addresses being able to insta-kill via direct damage, but still does not address the spell being an encounter ending spell. There are far worse things I can do to the frog than squish it.
I'm a little confused by the mention of 4E solos. They weren't very effective. What I hope he means by that is they're looking at the mistakes/issues with 4E solo design, and not making some of the same choices, but are instead using some of the ideas seen in the solos of later 4E books.
Erm... some solos weren't effective and others were.
I remember a Solo Shambling Mound that got a few characters killed (since it could absorb them (out of play) and if the shambling Mound took damage it split it between itself and absorbed party members and it dealt ongoing damage while they were absorbed.). Basically the party couldn't attack it while it went on its rampage and damaged them, the best they could do was action denial until the absorbed characters made their saves. It was nearly a TPK.
There was also the solo polearm Fighter with infinite OA's as a 'trait', and 'indomitable' which allowed them to make a save at the start and end of their turn (even against things that don't normally give a save with the normal +5).
I'd have to say a well built 4E Solo was a terror to behold.