I would understand you perfectly. The fact that you used "about to be" suggests to me that it might be just a bit more imminent than "future". Maybe someone with more knowledge of the Swedish language than I have could translate your sentence to Swedish if the meaning is a bit different than "I am your future boss"
This suggests to me that the "blivande chef' is going to be joining the company or department, rather than someone already there who is being promoted and now fills the role of my 'boss-to-be.
"I am your incoming boss" also sounds a little too formal and perhaps directive to me--if the supervisor wants to begin in a friendly, easier way, but that's just my take on it. ;-)