I have to admit that I was thinking that Illumina would fit fairly well as Keldors mother, ever since Emiliano revealed the first fussy details about her.
Prior to her creation I figured that a horrible semi-demonic witch like Shokoti would have been a suitable candidate as well.
I suppose the nature of Keldors mother depends on how you want to develop Keldors character, and ultimately the inner nature and motivations of Skeletor himself.
Do you want his mother to be good, or at least repentant? Then her relationship with Skeletor/Keldor would be highly complex, perhaps there would be a great deal of shame involved, for having a son that she ultimately failed miserably to raise into a good man.
Keldors mother would then probably keep this a secret from everyone, never speaking about her son, and would perhaps ultimately even clash with Skeletor. Someone like Illumina would work in that case.
The second route would be a relationship wherein the bad values, and possible mental scarring and abuse, that eventually leads Keldor to become Skeletor, would have been something that he gained from a cold-hearted and sadistic mother. A terrible person like Shokoti, that only craves power, and sees her son as a means to ultimate power.
In this relationship, the mother could have some form of twisted pride and liking of her son, that she would misinterpret as love. Keldor and Skeletor on the one hand, would have a more complex relationship to her, or may ultimately hate his mother with an unbelievable vengeance.
I see here that Emiliano had a different plan for Illumina than as the mother of Keldor, so it's possible he would have taken a different route all-together.
When it all comes down to it tho, the mother of Keldor could be one awesome and complex individual. And almost certainly a sorceress, because Keldor certainly didn't get his magical interest or talent from Miro.