I agree, redoing space seed could work well, the only problem I see with that is, they would then feel the need to do TWOK for the 3rd movie. That I wouldnt want I dont think.
I love this movie and I love the direction they took. That being said, I feel there is no other direction for them in the next movie other than Klingons. Seriously. Nothing says TOS like Klingon bad guys. We didnt get them in the first movie except as cut pieces on the dvd. We need Klingons. Heck even Enterprise started out with Klingons. They understood, if your going to do a Prequel to Star Trek you gotta have the best bad boys of all the series.
Other than the Enterprise and her crew, nothing is more recognizable as Star Trek than Klingons. Nothing is more Star Trek than Klingons. Yes you have your Romulans and borg and what have you. But seriously. Do they really compare to Klingons in our hearts and our minds?
Kirks biggest antagonists throughout the series and the movies has always been Klingons. They need to explore that.