I would love animation/imotion preview thumbnails a lot. Right now i have to use 3d exchange to preview my motions which require loading them in there time and time again, kinda harsh. 

That does seem kind of harsh. You do know that iClone will play those animations too, right?

Previews are something that would be helpful, but potentially be very slow and memory intensive. DAZ does pretty well with previewing the motion on a character when the motion is moused-over.

To preview right in iClone, just add your motion to your character by double-clicking it with the character selected, or dragging it onto the character.

It can't play them with a mouse-over though which would make it super convenient. Do you like adding a character then adding motions and deleting then it's more work. 

It is a lot less than sending them to 3DX!

You can cycle through them much quicker in 3dx. It would suit my workflow to have nice sized preview thumbnail. It may be irrelevant to you.