Freestyle on fixed - I don't get it

I meant the evolutionary process, sorry should've made that clear, what I am saying is that the process in creating a bike to fit a purpose (MTB, BMX, etc.) always start with something that wasn't designed for certain task.

before MTB arrived, it was cruiser with big balloon tyres for instance, and the design as time go by evolved into the bike we see today.
Right now I think that's precisely what the fixed gear trick bike is now, we're already seeing the process of using track bike to perform trick, and that encourage people to create frame to do these task (look at the Volume Cutter for instance, the BMW, Charge, SuperTed's Vans bike etc.)

right now it look silly and pointless to some, but give it time and we'll have a bike that bridge the gap between BMX and MTB.

Yep, got you now. I maybe just need to wait for the evolution but I think that would have to take a large directional change to come up with something between a BMX and an MTB from a road/track bike.
I personally like cruiser BMXs as they seem to fit the bill quite well. Can be ridden a good distance with seat up yet still agile enough to have fun on.