ZUN apparently said he had this in mind as Okina's original concept, but he didn't wanna do it wrong and end up offending anyone, so he decided against it in the end.

Part of me kinda wishes he'd done it. It's a cute concept.

Vid-szhite said:

ZUN apparently said he had this in mind as Okina's original concept, but he didn't wanna do it wrong and end up offending anyone, so he decided against it in the end.

The interview in question, in case anyone's wondering.

He finally went through with it in Visionary Fairies in Shrine chapter 14, which features Okina in a wheelchair (the going explanation in Western fandom being that Okina is one of those wheelchair users who has some independent movement).