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Splendid answer, thank you. My engineering mind won't allow an inferior solution at the expense of aesthetics; I had it in mind that the qr allen key skewers were failing due to thread stripping rather than failure of the skewer itself - not so?
I'll admit I hadn't thought about windup. I dare say a decent thread lube would limit this, but still it is a good point.
My £200 will likely be spent on a rear solid axle, a front qr Allen key skewer, and about £185 of wine gums, but I'm nevertheless curious about how you'd solve the problem given an unlimited budget...
(I take it the tap-axle-internally-to-receive-a-machine-screw mod isn't deemed sufficiently clampy for a horizontal dropout?)
Cupcakes-
I had it in mind that the qr allen key skewers were failing due to thread stripping rather than failure of the skewer itself - not so?
If the nut thread is the weak point, that could happen, but it would be easy to fix by using a steel nut rather than the aluminium alloy typically used. Once you eliminate that, the break would usually be at the first unengaged thread on the bolt part.
I take it the tap-axle-internally-to-receive-a-machine-screw mod isn't deemed sufficiently clampy for a horizontal dropout?
It might be, because it generates twice as much reaction at the dropout face as a skewer for a given amount of bolt tension. I haven't tried it, because all my fixie bieks have chain tugs.
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I'm nevertheless curious about how you'd solve the problem
Snug it up using the M5 thread as per a normal Allen key skewer, then hold the bolt head stationary with the Allen key and tighten the splined nut on the same end with a custom wrench to drive the nut towards the dropout face on the M8×0.75 threads cut on the outside of the bolt head and the inside of the splined nut. It looks like a differential screw, and would work as one if you turned the bolt while holding both nuts stationary, but by cheating you can use the big 8mm thread to pull on the 5mm shank without simultaneously applying any torsional load to the bolt shank.
gbj_tester
And anything which needs twisting as it tightens can never be as good; because you're winding it up and pulling it at the same time, the stresses get added up so they break at a much lower tension than skewers which are pulled tight by a cam. There isn't any magic by which somebody can make an M5 screw which can pull as hard as 5mm tie rod. There's a little wiggle room if you really had to avoid the lever by using higher strength steel, but Shimano skewers are already strong enough that no amount of material improvement will allow an Allen key skewer to catch up. I could design something which would have the appearance of an Allen key skewer which could be tightened to cam-QR levels of tension without applying any torque to the skewer, but it would require two tools to tighten/loosen. If your aesthetic objection to the lever is enough to make you spend £200 on a skewer, get back to me and we can talk :)