[Brightcolours]

      I ask myself why they only go to 1:2 magnification?

The lenses will become huge otherwise? You need the room for helicoids to move (parts of) the lenses even further way to reach 1:1. And the lenses already reserve a lot of space for the tilt/shift part. The same reason the Nikkor 85mm f2.8 PC-E micro reaches 1:2 max., probably.

 

Also, with 50mm you will get a very small working distance going to 1:1 with a TS-E construction. Something to consider. You will need ex extra 25mm extension would be required.

 

For the 90mm, you are looking at 45mm extra, and for 135mm 67.5mm extra.

 

The tilt is nice for closeups from for instance flowers, to get more of the flower in focus but with lots of background separation. Does one often need 1:1 for such things? Probably not. And if one does want it, an extension tube will do the job just fine.

 

The "outgoing" TS-E 90mm f2.8 reached 1:3.5.