SkyLake - big deal, this will give only 5-10% faster processor, maybe better graphics. i don't play modern games.
No dGPU - big deal, I have no real use if it. Same, I do not play modern games.
5400 RPM HDD standard - big deal, one can always upgrade to SSD. In my view, these fusion drives are more of a gimmick than something awful good. Never used one, never going to.
Soldered RAM - big deal. 21.5" is viewed as a home computer, graphics pros go for the 27" for many reasons. For home usage 8GB is plenty enough. Besides, RAM was not accessible even on the previous model, so it is really a big deal.
In summary - I do not see any shortcomings in this computer. If I take into account that I'd use it for at leat 5 years I do not think that $2000 (iMak 4k + 512 SSD) is very expensive, it is still cheaper than a 15" MacBookPro with similar specs. The current Apple offering fits perfectly my needs.
Note: my 2010 iMac is still pushing it well so that I am not really in need for an upgrade.