Been thinking about titanium. Odd, I know, but you're still reading. Ti has become more affordable since the supply/demand curve for aerospace/military applications has lessened, making it a much more affordable metal. It has some excellent properties, strength, flexibility, light weight, and corrosion/oxidation resistance. About half the weight of steel and about 50% as light as aluminum.

Thought, "Why hasn't someone attempted to make a motorcycle frame from this stuff, especially as mass-centralization and tuned-in flex have become important aspects of frame design?

Google showed me a few companies that make aftermarket Ti frames, mostly for Ducatis. These pics come from ARC Fabrication.

Pretty, in a minimalist/form vs fuction way.

Their Site