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But you're not applying the force in the same way.
In the traditional way the headset cup is supported on both sides, internally by the steerer tube and externally by the head tube. You have no support outboard of your cup because it goes over the head tube. I'm not an engineer but I can tell you your way is going to be significantly less effective.
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In the traditional way the headset cup is supported on both sides, internally by the steerer tube and externally by the head tube.
That's not right, in the traditional way the press-fit section of the cup is supported externally by the head tube (yes), but internally the steerer does not support it, it supports (if you can even call it that) only the cup itself which sits further up. With the press-fit section outside, forces are justed turned inside-out but the support is about the same. And the wall thicknesses (see my updated drawing) are higher too when it's external.
Of course it's always ideal if you use a 1" fork in a 1" steerer etc., but I am proposing a solution for a specific case that sometimes comes up here and there and I hope that people can take advantage from that, and the effort needed is actually quite low as it's really only about making the parts on the lathe. I will try the external cup now, thanks anyway for the input.
jetski
No offense but this is really not going to happen. Remember that there is the whole ahead force clamping it down. If the lateral forces would actually stretch the material of the cups so they get loose then this would happen with every cup in the world. But it doesn't.