If an airline is able to come out with better ways to increase their revenue without negatively impacting me - all the merrier.
I'd imagine paying a fee for a 7-day hold could be potentially worthwhile. The primary interesting point is how liberally they would make this available. While I'm sure there's almost zero-variation two months before a flight, there's a lot more ambiguity closer to departure. One week before? (presumably then it's an expensive price, and 7dayFee+cheaperPriceVs0Day might be semi-comparable to a 3-day out price or the like) One and a half week before the flight? Etc.
Many variables which could make this entirely meaningful, or potentially quite helpful at times. (And given there's a few relatively few would take advantage of this. So effectively minimal/no-impact on others.)