Much depends on what format you intend to serve your food in.
Will this be casual street food as in traditional yakitori or a sit down restaurant?
Where will your customers come from; a mall, strip mall, downtown lunch or tourist spot?
What reputation are you looking for; casual take away, fine dining, somewhere in between?
While I enjoy cooking and eating skewered foods, they only seem appropriate to me in a casual setting where it is socially acceptable to pick up the skewer and nibble the food off.
If the expectation is that a knife and fork will be used to eat the meal, then I usually find it odd to be served food on a skewer only to be expected to have to remove it myself. Is the point of your concept to serve all the food on skewers or will the kitchen be removing the skewers before serving, meaning the skewers will serve mostly as a cooking style?
Will the skewered foods be covered in sauce at service or will the sauce be on the side for dipping?
In any event, having skewered food exclusively would indeed seem to limit your appeal. A group deciding where to eat would by necessity have to all agree to eat skewered foods at your place. That doesn't seem likely to happen for most groups often enough to support a sit down restaurant, more likely in a location with lots of street traffic or a boardwalk where those who wish skewered foods can indulge while other places will satisfy the other members of the group.
In keeping with the yakitori style, it seems likely you would be cooking over a charcoal grill and since you are including other cuisines, having other grilled items would be an easy menu expander with little additional effort.
So without knowing more about your concept, I would have to agree with your partner.