It's going to come down to what the coach feels his team needs at that time. Chances are he needs singles players first. Most really good singles players can also play doubles. There's the doubles specialist exception, I know. Unless your something like Top 10 in your section for doubles and Top 150 or so in singles, don't kid yourself. Work on the singles and doubles game and let the results speak on their own.
On D1 teams you will sometimes see doubles only guys. When this is the case what I see in common is a big serve, excellent net play and strong returns. These players are the exception not the norm. They may not be in the singles line-up due to inconsistency or lack of movement that exposes them in singles.
I just hope that junior players don't get the illusion that their doubles play is going to be the thing that carries them to a college tennis scholarship. It could, however don't neglect developing as a singles player!