I think the obvious next move after the Dance is Dunk & Egg/the Blackfyre rebellions. There's some iconic characters and classic moments that people would be hype to see, plus a fair bit of mystery surrounding it, like what happened with Summerhall. There is the issue of GRRM still writing the Dunk & Egg novellas, so ideally he would finish them before the show ever hits TV... but it's GRRM we're talking about here.
All the shyt with the Long Night, Aegon's Conquest, Nimeria's escape, etc, is too far back for me to even be interested. I'd rather see the shyt we know about get fleshed out better than to see them try to make up the story around some old shyt. Prequels are rarely good. I hate when characters offhandedly mention some uninteresting mysterious event they won't explain, and then they break the mystery in a prequel by showing you what happened. No one actually cared about seeing Han Solo make the Kessel Run in less than 12 parsecs.