First, Congratulations with PB9 now out! Cheers! Just bought it - it looks good, many nice (and not so nice, lol) changes!
Second. Now that you have modern, optimized etc engine, please add possibility to see more layers of thoughts (children-of-children etc)! Really, even one more layer will be already big deal! If that will cause PB to work slower - OK, I can deal with it.
Especially now, when there is no Expanded view (yet?), it is very important.
P.S. And please make the font difference between 2nd and 3rd layers smaller. Now 1st layer thought and 2nd layer - its children / siblings / parents are nearly identical (not very good too), but! 3rd layer - children-of-children - are nearly un-readable. Or you should make 1st and 2nd layers really very big. Best of all is to make separate font size changers for layers, but at least make the difference not so big, please.
Btw thoughts name on the lower history panel are also of the main thought size! And thought pins on the upper panel too! This is definitely bad idea ), absolutely no need to make their size variable. At least, if you want to over-engineer it so, make separate scale for them in options too ))