Titanium can have problems with oils I've been told. Seeping into crystal defects and propagating. Typically I've been told they use polymer coatings to prevent the ingress. But with scratches and lubricants I think this would be much more common if it was a real thing.

I've always thought a spring bronze/brass frame would be fun. Even better modulus of elasticity, but the strength to weight is much worse.

Also keep waiting to see flash bainite frames.