Don't know yet. Right now they are just talking about starting one. Next year will be MLS's 10th in existence and reserve sides fall in the category of 'it's about time'. Some have suggested they play in PDL or A-league to minimize travel costs. Some suggest flying them with the full team and playing Sunday after the typical Sat Night MLS game.
Seeing as how no team that I know of has their own airplane and they just have the players fly on regular planes, this really wouldn't be saving any money, would it?