Doing anything other than working on Naxxramas is a poor use of time. There are a couple thousand people on K1 who have absolutely nothing to look forward to right now, because we've been clearing AQ40 for 3 months already. Based on the way this post was written, I have a feeling that almost no work has been completed on Naxx yet, which tells me it's probably a minimum of 6 months out still.
To re-iterate what Fei of Onslaught said, that means most of the guilds on K1 are going to have like 30-50 AQ40 kills before Naxx launches. Everyone will have BIS everything, and if you want to see the population of a server really drop, making them wait 9-12 months for new content is the best way to do it.
The best use of the development team's time, in order, would probably be something like this :
1. Work on Naxxramas
- See all of my notes above
2. Team visibility (change-logs, news updates)
- If you have the time to make a change in game, you should have time to write (at minimum) a 1 line change-log entry that is published on the website. Keeping players up to date with changes that are being made is important. It builds trust, it shows us what level of activity is going on, and it tempers expectations around future content/bug fixes. Without good communication you may as well not be working on anything.
3. Class-ability and talents
- I assume this has to do with fixing bugs with abilities and talents, and nothing more. These are important, because they affect everyone on both servers.
4. Fine-tune the current 40-man raids
- Getting 40 people together to raid is not an inherently easy thing to do. When there are bugs in this content, it pisses off a large group of players and wastes a significant chunk of time for everyone involved. Ultimately however, this content has already been released and it is playable, so it should only be looked at when there are major issues.
5. Fune-tune the 20-man raids and 5-man instances
- Same as above, but at a lower priority
6. Pre-level 60 content
- Only important really to new players, which I can't imagine there is a huge influx of. Most people on both servers are 60 by now, and if they made it to 60 once, they can do it again. I personally encountered very few bugs of significance while leveling
7. TwinStar Features
- Not blizz-like, shouldn't be a priority at all. This probably helps generate some revenue for TwinStar which I suppose makes it a bit of a higher priority for you all, but it really does nothing to help players, except by making account selling easier.
8. Gold/Honor-sellers
- Unless these players are exploiting bugs, such as duplicating gold, then there really isn't a ton that can be done about it. In-game GMs do a generally good job of banning the spammers from world chat. You can't shut down the websites, and you can't prevent people from using the same password on multiple servers.. so there isn't a ton you can do about this.
For changes not mentioned here, I think accelerating the release of content on K2 is probably a good idea, and subsequently at a pre-determined date, merging the server. I don't do a lot of BGs so I can't comment on the issues that are faced there. I imagine I would prioritize fixing BGs between 3 and 4, personally.