This is indeed theoretical If that wasn't obvious, I do not plan to fly a real rocket and slap a mechJeb unit on the side.
Assuming that It was provided with all the inputs it required and it was given enough control over the rocket, then I would assume that something like mechJeb would be able to fly a rocket in a real Enviroment.
But perhaps there are some values that MechJeb Is able to get in game that would be impractical to measure on a real rocket, or the fact that kerbal aerodynamics are much different than real aerodynamics and something MJ does would just not agree with our atmosphere.
I don't know enough about the mechJeb plugin to know for sure, But what I would imagine would be difficult would be getting the height from sea level as I am not sure if this is or how it would be measured for a real rocket.
What do you guys think would this work?