Why not? What's your top 15 then, eh?
Well, if you are looking so far ahead into the future, 2020, I think you'd project the historically great programs with big budgets to continue their grasp on the top-15 rankings. I have no reason to believe that looking back 10 years and not seeing Boise State relevant until about 6 years ago that in another ten years they will have sustained that success.
Off the top of my head, here are teams I would rank higher than Boise State not knowing anything other than who they are and the 2020 time-line:
SEC: Georgia, Florida, Tennessee, LSU, Alabama, Auburn
Big East: Pitt, West Virginia
ACC: Florida State, Miami
Big Ten: Ohio State, Penn State, Nebraska, Michigan, Wisconsin
Big-12: Texas, Oklahoma
Pac-10: USC, Oregon
Independent: Notre Dame
This is not even including the higher-end possibilities of current above-average/mediocre programs who can rise into some sort of "dominance-streak" like: UCLA, BYU, Utah, Texas A&M, Iowa, North Carolina, Clemson, Texas Tech, Oklahoma State, Michigan State, Virginia Tech, California, Washington to name a few. I would lump Boise State into this category, but I wouldn't even have them that high. The reason? Their budget may not allow it, they may lose Chris Peterson to another big-time program, they will have to compete in a new conference (changes may be heading their way competitively) and they may begin to lose their marquee games. They are not afforded a chance to mess up too often as it is NOW, let alone when/if that mess up happens in a sustained manner.
I'm not a Boise State hater, I think I just don't really care enough about them to argue that they are a perennial power when history shows us that it is often the case they are not.