Tbh, for me the Caverns of Time were probably the most disappointing instances in WoW. Small-scale battles shaped to look like key events gives more a feeling of historical fantasy pulp-fiction than anything FFXIV-related. The Option B only seems further cheapening, even indignifying.
[Edit: To be clear, I have nothing against creating more ideas or critiquing things in advance. I'm glad to see a post of this type, rather than continual corpse-beating on well-known, often bi-modal, subjects.]
Yes, we have, to an extent, time-travel, but we can only go back as far Echo can take us -- as far as existent and reachable memory. We are bound to the survivors of both the Eras and generations. While that seems limiting, I think it's been my favorite thing in the premise of FFXIV. We're a group of ragtag nations, practically children as civilizations would go, trying to grow up before we have to start again but without the knowledge to actually pursue that cause. Threat vague or unknown. Past knowledge, unknown. And yet the rest of the world might function normally around this fatalistic setting. But it's irrelevant to us, whose magic is at the mercy of these cycles of disbalance and the primals, a sort of paralleled manifestation.
Wouldn't then more relatable connection be in basically making something that can carry over between eras? It's unknown how much destruction is supposed to occur in each, but in either case, bridging the connections between eras, and between generations, such as with some manner of immortal memory, be only solution available to the Circle of Knowing?
The strange thing is that, although unnoticed, the solutions might already be in place, through both the primals and the beastman who worship them. We've been through 3 Umbral eras so far, and have 3 primals to show for it, if we count Good King Mog. I'd rather see those points of the world setting reconnected, and then develop theoretically first -- rather than the emphasis being on a quick concept for an instance.