Just noticed that MIP has launched new versions of their Race Duty Aluminium drive shaft kits, and this time with steel dogbones which should be a lot stronger than the aluminium ones. And there is no limitation to only 2S anymore.
MIP kit numbers are #13270 (rear) and #13260 (front).
Check these links:
As far as I can tell, the only difference to the X-Duty kits are the steel dogbones and the differential outdrives. So it should not be too expensive to go from the X-Duty's to the new dogbone type.