We would like to use video lower thirds with the title editor.

This could be achieved by having an option for a delay time for text to appear on a title. This is what it would look like in vMix

Multiview:
Layer 1 (Blank Lower Third)
XAML Title

If there was a delay, a blank lower third video could be used on the fly without pre rendering in After Effects.

Here is an example of what I believe it could look like.