Uh… not so much… I mean… I full on went into it here back when I was writing a lot of the next gen “Our Share of the World” ficlets, but basically… it’s not something that is compatible with my own personal headcanons of the involved characters.
And there’s also the fact that in my head it’s just: he definitely exists in canon Boruto which doesn’t have Shikako. (Also, also, according to DoS there’s basically birth control no jutsu which makes accidental pregnancy highly improbable).
I mean, definitely feel free to have that as your own headcanon for Shikadai; but it’s not something that I’d pick up for my own collection. I quite like the idea of Shikako just being Shikadai’s bewilderingly powerful aunt who is always on crazy adventures.
And I just really love the idea that Gaara would be the kind of person to adopt children leading into the next gen sand siblings (regardless of being in a relationship with Shikako or not).
Although even if Shikadai was biologically Gaara and Shikako’s, if he’s still raised by Shikamaru and Temari then I don’t see much of a story happening that isn’t needlessly “you’re not my real mom” or whatever which is unappealing on a huge level and also, irritatingly, maybe what’s going on with Sarada and Sakura? No, thank you.