Recently there have been announcements about new and improved ion
thrusters.

One of them was the Helicon Double Layer Ion Thruster, and the latest
one is the DS4G Thruster.

Each represents different improvements in ion thruster design. I would
like to ask -- are these respective improvements mutually exclusive, or
can they be combined together in complementary fashion for an even
greater performance boost?

Besides these, any other ion thruster improvements on the horizon?