The thing is, JR, that these examples are more popular, mainstream designs. They were animated, for the most part. Their release was only inevitable.
Things today, however, are much different. Bandai plan their plastic release along with their resin release. I don't expect to see a MG Powered GM any time soon, not to mention GM Cannon II, Zaku FZ, Hi Nu, et cetera.
While Terpfen may have exaggerated about the "never release", he's right in pointing out that we are as likely to see those kits in plastic within the next five years as getting a Gundam ver Ka. kit that doesn't suck.
The GM Custom and GM Quel were not unusual, given that they saw the opportunity with the MG Alex mold.
The MG Wing ver Ka. was the true oddball. Who would have expected a Wing ver Ka. in MG form. I believe, though, that the "Ka." line was made to cash in on Katoki's name, but the line was probably an afterthought after the GM Kai.