Yeah, the end user doesn't know what they finally included in this version, so can't tell what is delayed and what not.
Remember, they not only added GML changes (those mentioned in this topic and not mentioned), there are also Sequences, resource tree upgraded, data format changes, DND actions for nearly everything new, gml functions for sequences too, and there might be other small IDE improvements/addons (I don't have access to closed beta, but a friendly squirrel
said, that "I didn't noticed some changes, until get back to 2.2.5, and started to miss them. Nothing big, but sometimes a small change make a big difference.". My hype just raised, so sad that I don't know the details :/ ).
So, even if it seems that they have some delay, it's delay for GML updates only, and for whole 2.3 there's probably no delay at all, as
they decided to put much more that they initially thought year ago, and that of course moved the deadline. The issue here is that they didn't updated roadmap to include those "not mentioned" updates too, with new dates.
Also, take in mind, that even if YYG completed features for 2.3, if closed beta users said that something isn't intuitive, and need changes, they even could rewrite some part of sequences IDE or GML changes syntax, or even add something new not planned before - as that's for what closed beta was, and why there's a small amount of most experienced users.
Delay might be not because of bug fixes, but because of adjustments and new ideas, so we will be more happy with what we get in stable version. And even leaking any info (for example sometimes they hint something in comments on bugtracker, mentioning something is fixed in 2.3, when bug was for 2.2.x), might not be accurate, as they might have changed their mind even today.
I believe that after open beta will start, we will understand why it taken so long, and we gonna find some other changes/fixes not mentioned anywhere
There will be for sure a long "what's new" changelist.