This is my question, why do you need a remote fill? If your brake system is in good condition you don't need to be checking it all the time. If you have to pull a couple of screws up from the threshold moulding and lift the carpet to remove a little cover on the floor to add fluid when you do the brakes on your car, isn't that easy enough?
I have the master under the floor on my daily driver, yes it is kind of a pain to get to it but so is pulling off the wheel and front hub and drums checking the condition of the shoes. Cars had them under the floor along with the battery for years and years, is it ideal, no, but it isn't that big of a deal either.
Just my take on it.