I don't think they would be (or need to be) effeminate. It's more of an issue, specifically, with the dev team having a hangup regarding boys with bunny ears.
Seriously though, it's like I've said before regarding Yoshi's "having a rabbit male might be kind of weird" comment. This, along with the men of the dev team (the men, specifically, as stated by Yoshi himself) actually refusing to work on the bunny outfit for male characters because it made them "uncomfortable". They had to ask female members of the team to work on it, resulting in it taking longer. They made the women do the work because the men straight up refused. How wild is that?
Let's really unpack that; as others have said, we do already have skimp options for males in the game. Why is there an issue creating a skimpy variation of the bunny outfit for men? It's because, as Yoshi stated before, bunny boys are "weird" for them. You'd think they'd just make them somewhat buff bunny boys or something, but this is obviously a hangup for the dev team.
Bunny women and girls with bunny ears have long been something of a feminine sex symbol, or a symbol of femininity in general. For them it's uncomfortable to put boys in bunny ears due to the longtime associations. It's not like I think the dev team is evil, but I do think they conform to a trend which has its basis in casual, societal sexism.
They are under no obligation to give players everything they want, but it deserves to be called out for what it is.