Admittedly, rather than new Egis I'd almost rather see some primals just incorporated into various attacks, in addition to the current egis. For example, perhaps "Painflare" becomes "Ramuh's Wrath", and the attack summons a Ramuh Egi which blasts them with lightning or whatever. Maybe a new DoT (or one of the older ones) can be converted into "Shiva's Revenge" with some new ice effects and a mini-shiva. That way Summoners don't require new pets all the time (which might be difficult to differentiate mechanically) but still "gain summons" with their new skills. This would require some serious modifications to the class, however, and I can't see something like this happening outside of a major expansion.
As for the Egi glamours, I can't exactly blame them for putting it on the backburner. There are three major problems with Egi glamours from a prioritization standpoint:
1.) It's Niche Content: "Egi Glamours" is a cool feature, but it only applies to a small subset of players. According to the 2015 official census (http://na.finalfantasyxiv.com/lodest...e8ff1bcf34c5ae ) approximately 9% of job distribution is Summoners. You can increase it to 18% if you also include Scholars, but it's still a small subset of players that can even use it. It's actually likely significantly less than 18%, considering pretty much every level 60 Summoner also has a level 60 Scholar (provided they complete the class quests). Plus, you'd likely have to be lvl 60 to use the feature, which makes the users for it even lower. I don't know how the numbers are generated, so for all we know the actual amount of "Summoner Mains" who would use it might be even lower than 9%. It's a cool feature, but ideally they want a larger percentage of the games population using a new glamour option. Plus I can't wait to see the forums rage about how "this was included over X".
2.) It's Expensive Content: Believe it or not, it's incredibly time consuming and expensive to create new models and animations. In a recent interview, Yoshi P stated it takes 6 months to add a new outfit to the game, partially due to the altered models for different races and the like. Creating new, unique models (and especially animations) is incredibly expensive and time consuming for most games, not just this one. It's the reason most games use a lot of recolored or slightly modified enemies, because it seriously helps to cut down costs. Egi Glamours would be no exception to this (surprisingly high) cost, especially considering each glamour they add needs their own set of animations. This is especially true is they allow you to use any primal in any of the three roles. Currently, each Egi has Six different attacks / animations (including the summoning animation). That means that for each new/updated egi, they need to have at least six different animations, possibly somewhere in the 12-15 range if they want to allow them in any role. That is going to be far more expensive than it sounds. Admittedly this isn't as relevant for the Carbuncle, who'd only need around three more animations, but even that isn't cheap.
3.) It Might be Difficult: Lastly, depending on how the game is coded, it might be a significantly more difficult task than it appears. It's not necessarily simply "swap out model". Whether it be hard-coded, client-server data integration or simply poor planning this could actually be a very difficult feature to implement. Plus it would necessitate new menus of some sort, and a lot of more backend work than it may appear. I don't know enough about their code base to speculate on their difficulty, but working in the software industry has taught me that many times "simple" changes can be a herculean effort. They are likely dealing with a lot of old code that wasn't designed to make this kind of feature easy to implement. Once again though, that's just me speculating.
So, while I truly understand and respect the desire for Egi glamours, I also understand why it's not considered an especially large priority by the game designers.