This has been discussed on here before. Packs won't make a difference towards saving space for future content, as they're technically just a bundle of a bunch of individual costumes for a discounted price. Regardless of whether the issue is the total filesize of all the DLC or the total number of DLC items available, there is absolutely no difference either way.
Also, considering the fact that PS3 and 360 did not get the season pass makes it pretty likely that at least the last pack included in the pass will be beyond this cap-off point for DLC. There's no way to know exactly when, but it's pretty much guaranteed they will not be releasing the entirety of the season pass costumes on last-gen. And since there are no characters currently planned for the foreseeable future (at least not before June), it's all but guaranteed we won't be seeing any new characters on last-gen either.