I think a Nehru is very close to some of those (T-word) dress jackets and doublets with assorted stand-up or military collars. I expect you could maybe wear one in a more casual fabric in the daytime. I think moleskin might be a good choice for just about any cut of jacket. But I have some misgivings about a do-it-all cut.

What sort of shirt were you thinking about?

That make-your-own site is interesting. Have you done business with them?

Back to your original idea, though. Buttons are one of the cues to the level of formality, along with puckered seams, pocket design, exactitude of cut, overall sleekness... Metal buttons, like jeans buttons, say "work clothes" while metal buttons with your initials say "dressy" and cloth covered buttons say "very dressy". Zippers say "casual" or "work clothes". If you lose the buttons, your jacket's formality will depend in part on fabric, but much more on the shirt you wear.

To my way of thinking, unless you just have an idea that a particular cut of jacket suits your physique better than any other, you might as well consider a more casual cut to go with that more casual fabric and a sleeker one for the dressier fabric. Sure, it might be interesting to have a "trademark" look, such as the Nehru-Mandarin, but one tool can only do so many jobs truly well. Daytime means pockets for toting stuff. Day dressy means some middle ground and nighttime formal means minimal cargo. Your trademark look may be in danger of having too many pockets or not enough.

Consider how a velvet jacket cut like a Levi's cowboy jacket would look- yes, dressier than denim, but not quite up to true evening wear- not with tabs at the waist and those vertical seams and pocket flaps, much less with puckered or welted seams. Similarly, a "Barracuta" jacket made up in tweed doesn't look as dressy as a tweed sportcoat. Did you ever see a denim blazer?

Think of the subtle differences between/among barn jackets, chore coats, field coats, bush jackets, and sport coats. Collars/lapels and cuffs are probably the biggest cues, but what about belts and pocket flaps or pleats? Will this jacket be expected to keep you warm? What distinguishes a black blazer from a tuxedo or a white one from a dinner jacket?

Consider also the differences among uniforms- cavalry breeches are intended to be functional, but you really wouldn't want to go into battle with too many capes and cords hanging off you. And I wouldn't want to try to carry much in the pockets of a Dress Mess outfit.

I'd like to put in one last vote for moleskin. I have seen some military cut jackets- four patch pockets with flaps and a stand up collar- in washed moleskin that look to me like they would go well with a kilt. I have a regular Saxon navy moleskin blazer that I am thinking of converting. It has open patch pockets. But I will probably go ahead and put on square silver buttons and cheat it into evening wear on some occasions.