This would be nice, you should also be able to select different champs for each role too. Like if I want to play jung or support I wouldn't want to support with Yi.
I should be able to que up with jungle Yi and support Braum, for example.
Riot's already confirmed they're working on Team Builder Draft, in which you queue up for two positions before proceeding into pick/ban phase. I think it's tentatively scheduled for release during the pre-season.