I don't think it's practical to have a key tweets only thread.
Here's why:
1. What is considered a "key" tweet is a matter of opinion. What one person considers key, another may not. And vice versa.
2. If such a thread existed and was strictly enforced resulting in warnings and bans, that takes the fun out of posting on this website. No one likes to be told not to post something they wanted to post. As long as the posts are in nature to college sports conference realignment, it should be fair game.
3. If something is truly key/monumental, it is only natural that posters want to immediately respond to what they just read. If a future key tweet was "UCONN TO THE B1G IMMINENT" how many would honestly not immediately respond to that post? Would you realistically be like, "yeah that is a key tweet! I will now exit out of this thread and go into another thread to share my joy!" Not likely.
4. As has already been mentioned, it is not hard to just scroll past user comments and only read actual tweets. I've done this before when I wasn't interested in the particulars of the back-and-forth conversation at the time. It is no big deal to me to simply scroll past what I don't want to read, and it shouldn't be a big deal to others.