Increase glamour plate limit.

[Bonbori]

I really need to repeat, while I personally would gladly wait an entire year for them to overhaul and fix the underlying systems of the game that constantly limit what they can improve and implement... I will bet a kidney that most of their subscribing playerbase would absolutely desert the game, if only to wait till they "fixed" it. And that would deny them far too much revenue to make it an attractive option for the people who make the financial decisions.

I don't think anyone is disagreeing with you on the fact that, realistically, MMO development is a balancing act aimed at retaining the largest possible playerbase month to month.

However, I feel you grossly underestimate the amount of resources SE has at its disposal. It's not even conjecture - we have seen clear evidence that they have the resources and manpower to commit to short-lived and catered to niche audiences (by Yoshi's own admission @ Eureka) content like Diadem, Eureka, Verminion and Rival Wings, just to list a few off the top of my head.

They can do that, time and time again, without compromising any of the core content that retains the majority of the playerbase, that being MSQ and casual 4-, 8- and 24-man content as well as, to a much lesser but still comparatively substantial extent, Savage and Extreme.

So... no. I do not buy for even a nanosecond that SE would have to sacrifice a noticeable segment of their playerbase if they decided to skip another iteration of Diadem for one expansion and instead reassigned those resources towards perfecting the game's glamour system (and resolving any related server or engine-side issues in the process).

TL;DR: If SE can waste their employees' time on Eureka, which was intended for a small subset of players and relevant for only a limited time, they could just as well waste it on finishing the half-baked glamour implementation, which would add lasting value to the game as a whole.