Is there more of this stuff? I absolutely love it.
Consider 2 things:
1) A Speedbooster can never (!) work from-to the same mount. No EF-EF, no MFT-MFT. Just a limited amount of combinations allow speedboosting, like EF-MFT, NF-MFT. So your lenses are going to stay exactly the same.
2) The BMCC has a passive mount! Big drawback as it means none of your non-manual lenses are going to fully work on it. No iris control, no Power O.I.S.. And of course, each of your lenes is going to get a tighter field of view due to the smaller sensor size. You need fully manual lenses to actually use this camera to it's fullest potential!
2.5) Even with an active speedbooster, you won't be able to electronically change the iris of an adapted lens (so a Sigma 18-35 is always at f/1.8) or use Image Stabilization (like the really good one on the Canon 24-105 f/4 L).
I ran into a BMPCC pretty much blindfolded and aside of battery, memory and low light issues, the proper usage of glass is a serious thing to consider! Don't run into that if you don't know anything yet. Also, I'd rather suggest the GH4. 4K, 96fps and cheaper while retaining all of your workflow and the way of using your glass. Just saying.