Any material has a fatigue limit, titanium alloy could have higher fatigue limit than Cr-Mo steel alloys, comercially available titanium are alloys of 90% tianium mixed with aluminum and vanadium, various ratio changes the character of the material.
The titanium 6AL-4V alloy accounts for almost 50% of all alloys used in aircraft applications, most like in small parts as blots and axles. The 6AL-4V titanium is less dense, hence more brittle than the commonly used frame tubing material 3AL-2.5V..
Using titanium alloy for pedals spindles isn't any worse than using aluminum for airplane wings, usage just need to be monitored, then again how often do you actually monitor your pedal spindles?