I got my own pressure advance feature to work, better than my JKN implementation for Marlin or the advance feature already (broken) available! It’s like christmas for me 
I printed two identical test cubes: 20x20x2mm, 0,2mm layer height, 80mm/s print speed for everything, 500mm/s² accel.
On the left you can see the one without advance (k=0), on the right there is the cube with advance (k=250, I’m using integer calculations for speed). I think the pictures and the dimensional tolerance increase don’t need more words - the k=0 part has the rough top infill due to the high speed, the other one is smooth as skin!
Here you go: Pictures
See dev thread on github for details.
In some days, only the ability to melt the filament of the extruder is limiting your print speed 