I don't know what the Geforce 3 uses but <b>if<b> it doesn't use AGP Pro then, no you would not need it.
I have no idea what will happen in the future. The trend does seem to be that video cards need less power than their predecessors. However, who knows what future features may be added which might require more power? Lot's of memory, possibly.
If I were to guess, AGP Pro will remain with the high-end cards and manufacturers of mass-consumer 3D cards will not quickly adopt AGP Pro because most of the consumers do not yet have it.