I think competition is not a high up factor on this.
I have seen market 1,2,3 exchanges all picked, and there is certianly market 3 exchanges (which have VM cable) not on their list.
The factors I have noticed are.
How affluent the area is.
How much properties in the area are commercial.
How close cabinet is to exchange,
Viability seems to be measured per cabinet rather than per exchange, and my guess is a exchange needs X amount of cabinets to be viable to be considered.
Edited by Chrysalis (Sat 08-Jan-11 23:04:34)