Started with this:
The tricks are to get 2 diagonal MIS starters in place (using either RHW-4 E1 or diagonal RHW-4 A1 ramp pieces, in the old Ramps tab ring), remove the stubs of L1 45 degree MIS FlexFlys, and draw the DxD crossings half by half. The FlexFly stub needs to be removed because it seems to require more space to be able to make the crossing. Watch this step-by-step gif (duration 60 sec.).
The first generation result.
An RHW 4-to-6 transition piece (upper left) was too close by the FlexFly crossing. This is how to convert these two crossings correctly.
After the first build, I thought the acceleration and deceleration lanes were too long (10 tiles) according to Haljackey's guide, so I moved the transition pieces nearer (6-9 tiles). This is the final result.
The MIS loop transition plus DxD crossing turns out to resemble a loop ramp very well... and save much space.