In my experience, staffs generally use the bye week(unknown opponent) to rest, get healthy, self scout and focus internally on working out any kinks and doing what they do better. To the extent potential opponents run similar offensive and/or defensive schemes they might get a head start by practicing against the base and/or some film study of base alignments but, as far as real game planning and dedicated practice reps to a specific opponent that would be more unusual than common place, as it is generally more effective/efficient from a practice time utilization standpoint to focus on what you KNOW you need for an upcoming game rather than what you MIGHT need for an upcoming game. As with most things, nothing is absolute and there could be some exceptions, if a potential opponent has a scheme, player, etc. that is unusual there might be a limited focus on specific situations in the bye week. The distinction is whether a weekly practice plan is geared to a single opponent or more general in nature with a couple of individual periods devoted to more opponent specifics with the latter being much more likely than the former.