I don’t think the Silent Hill HD analogy works at all tbh. That one was a straight port of a game that already had voice acting. The new voices used the same exact script. Adding the option to play with the old voices cost nothing at all. FFVIIR is a completely different game based on an entirely new script, with the original not having voice acting at all.

A more apt example would be Catherine Full Body which, at least in the Japanese version, added “Dream voice” selections for the leads, including popular voice actresses so you could customize your Catherines. Still, I’m pretty sure it’s just the Japanese version and it’s a pretty unprecedented case. I wouldn’t say it’s feasible for FFVII at all. Personally I don’t even get why people would want that so much, but that’s just me.