W/r/t "Not a big enough base of potential customers to keep anything but the most basic replacement block, if that. Everybody wants something custom."

True, and not mentioned often enough: the greater the number & value of features, the fewer that will be sold - and most expensive.
The best money maker is (almost) a direct replacement: highest volume + easiest to design, but offers the fewest advantages.
Needless to say, this dilemma has screwed up the development of many interesting projects (slant 6 aluminum head). It will be faster if it is cross-flow, but there are no manifolds... You get the picture.

Everyone means well, but no one entertains such a complex operation except to make money, and (as we all know) the best engineers are not always the best project managers or accountants.