While I would agree that a boost controller would be fun, it would not be very realistic.
When you raise boost pressure, you are increasing airflow. When you increase airflow, you need to increase fuel flow. There are also constraints as to turbine efficiency and how much any specific motor can handle. Timing must be altered sometimes, as well as may other things.
What I would love to eventally see with the game is an engine management system that is user programmable so we can alter the performance of our cars. We could monitor Knock, O2, EGT, Oil and or Water Temp, Oil Pressure and whatnot, allowing changing of fuel trim, spark timing, boost pressure. That would be great.
I also doubt it will happen. I'm sure it will happen in a game/simulator some day, just not very soon, and definately not in S2.
I enjoy the realism of this game, so it ouwld be great to get that sort of thing for it down the road, but I am not a developer and I'm sure that something like that would not only take alot of development time, but it would also take alot of CPU power just to run the game.
So while I say it would be fun and I would play with a boost controller, it would not be realistic, thus it's not likely to happen.