The well known “Numerical Recipes in C 2nd ed.” talks about how the first edition promoted exactly this - offset the pointer after allocation and you can use any indexing origin you want. And they promoted 1-indexing and wrote all the algorithms as such, before switching everything to 0-indexing for the 2nd edition.

I agree with you the subtraction instruction is not exorbitant, especially considering malloc is much more expensive and always has been.