Ahh. Yeah, I had a similar thing with another game where I figured it'd be better not to have an additional distraction.

Tbh, I saw this one coming a while ago. The best way forward, imo, is not to release tbc but rather just make new content ala osrs did. Ofc, it's a lot to put in to make new stuff, but if there's a significant enough playerbase, I don't see why not. Heck, they could just use maps and models from other expansions and just pallet-swap it, you know?

If itemization and powercreep is an issue, just make everything from vanilla content immune or resilient to the new stuff. That way, you can choose to try out new content or stick with the old without the need for character transfers or w/e tf.