I did some testing on puppets to see if I can fit 3 Truethrustcombos in the bufftime from Heavy Thrust by stacking skillspeed.
It works sometimes when I am at 2.28 or 2.29 sec GCD, which is a bit surprising since by dividing the 20 seconds from the buff by 9 you get 2.22 seconds. But apparently it starts working earlier! (Not reliable however)

I think with better gear it might very well be possible to pull rotations off that uses 9 actions after HT.
For example: Chaosthrustcombo - Phlebotomize - HT - TTTTTTTTT
No clipping issues and the rotation would be very simple.

I didn't do the math yet, but I expect it to be very good since Truethrustcombo has so much direct damage.