That's nonsense. Spending twice or three times as much for a system whose power isn't needed doesn't make sense, neither for the people using them (NOISE!) nor for the people paying for them. Use an adequate machine with a LITTLE headroom now, replace with a then-current (and inherently more powerful) solution when needed.
Also technically, rewind a few years and see how far the "future proof" promise has ever actually reached - particularly with Intel; but even with AMD, platforms mature and vanish much faster than people's needs for processing power grow. Expect next year's updates to be complete system replacements, no matter how much premium you spent on a "future proof" mainboard.
Besides, K7S7AG does support 166 MHz CPU bus.