>>How long do you think it will take until the paper begins to exhibit signs of wear?

Probably will take a while, although I admit I haven't had the patience to try.

The question is "what happens if you flap a thin sheet of aluminum or titanium the same way" ? Do you get the same change in physical properties, or more, or less ?

As far as I can see the break-in phenomenon / myth seems to be limited to metal drivers.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8