I see negatives with not much to show for gain.

I've been shooting 9.3 bore doubles long enough to remember when 9.3 bullet selection in the US sucked. Those days are long gone. We now have everything from the 250 grain Ballistic Tips to the 320 grain Woodleighs. The only advantage the .375 diameter has is the ability to buy bullets off the rack at the local sporting goods store, rather than having to order them from Midway, Huntingtons, etc., and I ususally order bullets on line anyway. Just about any variety of 9.3 bullet you could possibly have a need for is available now. The 286 grain 9.3 bullet has the same SD as a 300 grain .375 bullet.

Any 9.3X74R based wildcat will always be much harder to sell than a standard 9.3 and more of a pain to load for. Brass for the .375 Flanged Magnum has always been a pain in the ass and always will be. Brass for the 9.3X74R is easy. It makes more sense to stick with the standard 9.3.

By the way, your proposed name for your new wildcat has been in use for 107 years. .375 No. 2 Flanged is the correct name for the 320 grain loading of the .375 2 1/2" Flanged Nitro Express. The 270 and 300 grain loadings of that cartridge are known by the latter name.
--------------------------------------------------------------------------