Then it turns into a "how much hard drive storage inside?" question in which no one wins except the small subset that happens to get close to the size they want at the approx. price increase they want. Everyone else is going to gripe about "too small" or "too much" and "I don't want to sync when I have perfectly good storage on my Mac and can stream" and "I don't want to pay more for an on-board drive that doesn't have enough storage", etc. All of these were gripes that constantly flew when the "1" was the one.
I don't think Apple solved that problem by arbitrarily dismissing the internal storage (though the price gripers were happier). Thus, I believe the answer is in normalizing that USB port and letting those wanting to sync attach whatever level of storage they desire and those happy with streaming don't have to pay up for storage they don't want. OR, turn on some NAS discovery features so that the
TV4 or 5 can discover media on network attached drives (maybe hooked to an AEBS or Time Capsule).
As to power conservation, there are plenty of attached storage solutions that spin down when not in use.