IMHO, the bull barrel on the Karma guns is a major improvement and step away from the FX barrel design and more important than the Karma guns regulator configuration. We will see how the Karma, Red Pandas place at PAC.
The FX Dynamic action, with it's external plenum, is another important change. You, the owner, are not recommended to change barrel length or caliber, don't mess with that external plenum. You must have an FX dealer do that work. So, not as flexible as the other FX models. Using the Dynamic action across more FX models would make manufacturing easier (less complex) for FX, but I believe they do the vast majority of their manufacturing using CNC machines, that should reduce the benefit (cost wise).
If FX does develop it's own bull barrel, that upgrade would have to be done at a FX dealer for your Dynamic action rifle (my guess, but it is a reasonable one).
It is hard to say how many more near term (6 to 8months) design changes FX can handle without risking quality issues or heading off in the wrong direction.