First of all, you'e making too much of the bent/broken axle issue. They happen occasionally, but it's not like the existing design with a 10mm threaded axle breaks every day. In fact the broken axle issue only became more common after the move to 7 and 8s, but even then it's not like they break very often.

Axles break and bend for different reasons. Bending is usually then result of a single event, or non parallel dropouts, whereas breaking is a metal fatigue issue as I described earlier. Even then it takes a while. I'm riding an 8s freewheel on my commuter and axles last about 7-8,000 miles of crappy roads, potholes, and short steep hill climbs. When they break I can continue riding (don't even know they broke) because the QR skewer keeps them together. Usually the only evidence of a broken axle is creaking under load, or they fall apart when the skewer is removed.

But if you're determined to go your route, understand that the material demands of the bearing race and axle are very different, and they cannot be made with a single piece of metal. The bearing want's a very hard surface which can be made by case hardening, or using through hardening steel. Either produces very hard parts which wear well, but is brittle and highly unsuited for a load supporting axle. By contrast, axles require high strength steels such as CrMo, heat treated for maximum toughness, rather than the nhigh hardness called for in a bearing race.

Keep life simple, just make or buy axles of the original design, or incorporating my earlier suggestion to eliminate the end of cone thread. If you want to make a super axle, leave a support area or seat and grind out you're cone's threads and press fit them together.