During the 2 month gap due to Covid they reran a bunch of LLs from back in ARR with Yoshi-P in chat answering questions and commenting on things.
Apparently in the 2.2 one there was a discussion in Chat about Egi Glamours with Yoshida chiming in reaffirming that they are still happening.
Quote from the r/FFXIV discord.- Egi related conversations were touched, but unfortunately YoshiP didn't comment any further. "That is still something to come in the future", "We can't talk about Egi yet" implying that yes, something related to Egi (glamour? new Egi?) will come in the future, just unspecified
Your timeline is off by quite a bit, Carbuncles were added in late HW, which was early 2017, so less then 4 years. Which is still quite a bit to be fair, but it's important to note that Egi Glams wouldn't be a high Priority item and according to what we know about the Dev process would be the a thing they only really have time to work on when everything else is done. Of course thats gonna take time, especially as they'd have to create models, Attack Animations and figure out ways to deploy the system in the first place (as the initial system is a simple model swap but they'd need one that'd allow them to swap out attack animations as well).
That said, between the Blue Magic Spellbook as a template and Egi Assaults they theoretically have everything they need to make it happen.
If anything it wouldn't surprise me if they introduced EA's partially for this purpose.
Companions are a somewhat different beast, they were last mentioned during ARR afaik and then fell under the radar until Yoshi-P confirmed the guy who was responsible for that system was moved to another team.
Egi glamours on the other hand have been mentioned during Interviews and such at least once a year since their initial release, and usually reaffirm they still want to do it, its just taking them a bit.