Personally, once this does (eventually, I know) get sorted out, I'm hoping instancing is an OPTION... to me, instancing is a great way to just eat server resources like crazy.
Maybe something like you said, a "next in line" type thing, with the zone being able to be locked for a group (or globals used to temp flag players to be "allowed" to go in for that adventure but nobody else until it resets)...
IMO, LDoN was horrible on Live, boring to the max, the rewards blew, it was redundant (all the zones looked the same)... and was the most pathetic attempt at a time sink since Luclin. LDoN convinced me that SoE hired chimps to just bang out cookie-cutter content for profit. People only played it because they were desperate for solo and group content, because SoE made SURE that only raid guilds could advance previously. Does that make LDoN good? Nope. It's probably the worst expansion they ever did.
On live, LDoN is a ghost town expansion... as soon as missions came out, people dropped LDoN flat. Everyone knew it stunk, everyone I knew hated it. To me, it should be the lowest priority to emulate especially since far more important things (like AAs, tribute, leadership even, class balance, etc.) still do not work. Even pets still aren't working right. This is the stuff that needs to work first, I think. Not some expansion almost everyone I ever met hated with a passion...
If you want instancing, I'd rather see missions and mission zones worked on before this turd of an expansion. I'd rather use the LDoN zones as static zones, chain them together for massive raid crawls or something (which makes a lot more sense to me, you know, like a maze of twisty little zones, all alike
... or even swap many of them out with custom (openzone) zones.
I mean this is JUST MY OPINION, but the deeper I can bury LDoN on my server, the better.