Is there a notion of holonomic D module which admits the six functor formalism in the world of twisted D modules?
Recall that twisted D modules on $X$ are well-defined for any $T$ torsor $\tilde{X}\to X$, see e.g. here. The twist is by a character $\chi$ of the torus. Of course the most important example of this is when $X=G/B$ is the flag variety of a semisimple algberaic group.