The only real thing they could try to do is to try enforcing video/IP speed cap. They probably don't due to false positives - for example people jumping around a long video also make may "range" requests.

And the other approach is currently in progress - soon logged users won't be able to view videos without watching(or at least displaying/downloading) adds, so the logical next step is to nerf anonymous(as is without google account) viewing. No matter how I look YT has exact problems (and solutions) as all file locker sites. The only difference is that YT is not at mercy of Ad companies, it is the Ad company(at least Google is). So they might try some more aggressive measures, that normally would get a site banned from publishing ads.