I don't see why everyone shouldn't have romance. Shiki, Wiesz. Go nuts. It makes the story even better, IMO
Shiki is pretty primed for a romance subplot or three in my opinion. He's a hero out in the world seeking relationships(friendship) so it's pretty easy to tie a couple special relationships into that.
Wiesz I see as being the sort of character more suited to "best freind in romcom" romance. Where it always falls flat except for the one girl he shows no interest in. That that kind of just ignites at some point. That would be a great romance plot for him.
Weisz a Romantic Subject?
I would call it Lustful and something Vague.
Look, remember that Shiki grew up on a planet where he was supposedly the only Human being, something weird about that, now that I think about it.
The point is that Shiki is growing as a person, and in his own way it is wiser than many twisted people who have forgotten the value of life or the heart.
So give him time if Mashima wants to do it well, with Harem or without Harem, he needs Shiki to experiment with Homura or Rebecca or any other girl what is Affection and affection, unlike Weisz who looks for him more with Lust, besides Shiki It makes more impression face with the Sensual things than perverted faces, Being exact Shiki has a Very Adventurous Curiosity for the Female Gender, and an energetic Entuciasm for her Beauty there is almost the same as Weisz but Shiki would not force things so much, as Weisz to get something.
Just let this very unique "Adventurer" crew grow.
But if a NaLu 2.0 would be silly.
And I could do something much better, if Mashima can do something better than that.
Of course it would be good if after defeating Drakken Joe and cleaning the Shooting Starlight Guild, that is to beat Noah Glenfield, who looks like a Young August, I compare him to August The Wizard King in Fairy Tail, because he looks like a little at least when August was little, in case you don't remember he is still the Son of Zeref and Mavis, Biological Son.
Well, the point is that after they defeat them, it would be good if they travel the Cosmos Sakura and visit their natal stars or natal planets.