In the latest version, you can choose to roll for HP up to level 20 - instead of the flat and nerfed regular bonus.
The way it works for me, is that it grants the hit dice, but not the constitution bonus past level 9. So a fighter gets 10 hp at each level from level 9 to 20. I dont know if this is intended, but would it be possible to add the con bonus as well?
and perhaps add more options - for instance continue until you reach the level cap?