These keyframe interpolations graced Vegas's animations for the first few years, although they were very low in easing amount, and almost linear. 
But over the course of more than a decade, the 6 keyframe interpolations have fallen short of what modern users need for easing animation. 
The mediocrity of the keyframe interpolation affects the play of some excellent functions of Vegas. 

• 3D Parent/Child track motion : The 3D Parent/Child track motion is actually the 3D camera fo After Effects or Vegas Effects. Vegas is the only one NLE which possess 3D camera feature, but there is so few keyframe interpolation of Vegas that the Vegas' 3D camera animation looks stiff. 
• Mask : Mask is the most important part to do Motion Graphis / Lower Third animation / Reveal Text, Similarly, the lack of keyframe Interpolation causes Vegas's Mask animation to look stiff and linear. 
• Transition Progress Envelop: Transition Progress is also a great unique feature of Vegas among all NLEs. It can bring a different progression curve to a lot of old transitions ( some of Pixelan, proDAD, NewBlue & Vegas native transition ) and give them new life. Similarly, the lack of keyframe Interpolation prevents it from fulfilling its potential. 

If we can add more keyframe interpolations to these Vegas features, they will inspire even more potential!