I don't believe that is necessarily true. I believe it is entirely possible for such an arrangement to last. After all, humans do have finite lives, and humans are quite capable of maintaining strong desires long term.
You are correct, humans are not pets, and what I seek is not a pet, but a maid.
As for living their own lives, I have no wish to totally monopolize their time; I am more then amenable to the maid having her own life, and indeed, as my OP shows, I wish to aid them in living the life they wish to live, whatever that may be. I live in an area in which nearly any activity or desire can be fulfilled, from a college education to a BDSM dungeon, and everything in between. It would be best if this situation was mutually beneficial, and the maid assisted in living my life to the fullest, and I assisted them in living theirs.
Race is entirely negotiable; I have no particular problems or hang ups in that regard. Body type is also negotiable; as long as they are healthy, and willing to become attractive to themselves, I see no reason why a specific body type could not fit this role. As well, I'm willing to pay for everything to get them to that goal; there are athletic trainers in my neighborhood.
As for personality, I am flexible here as well, as long as they are willing to accommodate the parameters of my scenario. Demure and chaste maid? All the better to corrupt. Bratty and lively maid? All the greater to put into her place. As long as the maid is willing to be a maid, I could accommodate nearly any personality type that is not a danger to myself or others.
As indicated, the most important thing is attitude and eagerness; the rest will definitely be a learning and growing experience for both maid and master.