Bah! Now I see it in yet a different thread- enable time remapping - right click the clip in your timeline, select Time > Enable Time Remapping - THEN drag your Out point as needed.
you don't have to change the fps speed to get motion blur, timewarp's shutter blur set to manual shutter would re-apply optical motion blur similar to the reelsmart motion blur plugin.
but if you wanted a higher fps, then yes, Choose Layer > Frame Blending > Pixel Motion would do the trick in a higher fps sequence.
Yeah I should have specified that I was aiming to slow things down just a touch as well. For whatever reason, when using only motion blur, the footage was still appearing as slightly sped up.
For me, the original question was, how do I preserve the full clip at half speed. Answer: Enable Time Remapping on the clip. Drag the clip Outpoint to lengthen as needed.