When DoF went live, they linked that with LU 13, which changed the playing field for illusionists (although only briefly before they nerfed us again). I'd like to think that they would link the next "fix" for illusionists to KoS release. That way even if the expansion isn't any good or unfinished, I'll at least have something to look forward to
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Seriously though, based on:
-the resources that KoS has to be drawing
-the low population/outcry from the enchanters
-little hints from BG and others stating "code change" and a few other long term items
I would tell you not to get your hopes up on an enchanter fix for the expansion. So, to answer your question: buy it if you want level 60-70 content. Don't buy it expecting new illusionist fixes.
Zebsen