Additionally, map rewards were fine tuned after 6 months, with the daily chests for meta completion being added among many things.

I think the real issue is that they tried to over-hype the expansion to convince everyone to spend $50.

Case-in-point: Legendaries, as you mentioned. Sure, I have no doubt that we'll EVENTUALLY get all 16 "HoT" Legendaries. I'd be surprised if they require Expac 2 for ones released later. (They'll probably still use the current system allowing HoT currencies & Unbound Magic).

Likewise, we'll eventually get Legendary armor (but this probably will require expac 2... Because they'll probably hold new raids until after it launches.)

The real issue is that they had to justify $50, when it was mostly a revamp of features setting the groundwork for what we have now.

(Likewise, it unfortunately means that we're unlikely to ever see another massive overhaul like HoT brought.)

They've shown that if they focus on creating content, they can do it well and on a fairly good schedule.

Given that LS teams have given us 4 new maps (likely 2 more before the next expansion) designed from scratch... I'd be willing to bet Elona will be fairly fleshed out. (Granted, the LS maps don't really have metas on the same scale as Dry Top, Silverwastes, or HoT maps... I don't really see that as necessary for all maps.)