It would be nice to see some progress made on the interpreter but I think it's to Ruby's credit that the language design hasn't changed that much in the last several years. A lot of the activity on the Python side has been fixing things that weren't well thought through in the first place.
Honestly, I'd say the opposite is true. The more the language design changes, the more implementor time is going towards servicing the changes and not squeezing the fat out of the implementation.
That being said, the two often occur together because changes are exciting and attract effort.
I don't see how that follows at all. If the biggest issues with Ruby are performance and memory management how does changing the language spec help fix that? If anything a stable language spec should help nail down the bugs in the engine.
