I visited a galley design and construction company in Europe during work on a new aircraft type some years ago - I'd suggest that you do the same, it was fascinating.
The interior size and shape of the cart is actually driven by the spec of the contents: From memory, there are three standard design sizes - KSSU, Atlas and BA's own bespoke (this may have changed). For example, you can't fit KSSU trays and equipment into Atlas boxes and carts, and vice versa. If you're going to change to a unique dimension set, you'll need to persuade airline customers of the benefits, as complexity (therefore cost) is being added. Overall galley dimensions, structure strength and maximum weights tend to follow on from the carts (or the other way around) so further re-design might be required.
I visited the testing area. A very nice, very elderly chap in a stained white overall dropped a loaded cart from 2 metres, set fire to something inside and generally knocked seven bells out of the cart. He then politely explained that despite all their best efforts to test and simulate everything, there is no known destructive force on earth like a 5' 8" stewardess. He said this wearily, but with some admiration and affection - I liked him.
BTW - "Carts", never "Trollies"