Why does everyone like to put libertarian-leaning Republicans in the Libertarian Party? I seriously doubt a then 40-year-old Justin Amash would leave the party--thus basically giving up his job, the establishment would never let him stick around, they already can't stand him--just to get 0.5-1.0% in a general election.
Amash will probably be the next Republitarian guy after Rand's done. Whether that's 2020, 2024, 2028, or even 2032 I'm not sure, but I have a feeling he's next in line. Only 35 now (shares a birthday with me--which is awesome) so it's not like he'll be in any hurry.