Agree people from Slate are probably looking for something more serious. The parodies and sarcastic goofy videos are something you see more in the Fray than on Slate, however there seem to be a lot of them on SlateV. Maybe it's just the ones I saw. Maybe they should be clearly marked as "funny" rather than "news".

You might consider having a section for Headlines that links to videos on other news sites - the quality and frequency of videos on news sites is poor, so by doing some editorial filtering you can provide a value-added service. However this may be a short-term opportunity as networks focus more on the quality of their web video offerings.

I doubt people are expecting much different form what is on Slate (which may be a difficulty for you if you wish to expand in another direction - the joys of branding). Alternative editorials and looks at regular news. In-depth treatments of important side-issues or behind-the-scenes-issues. Coverage on topics that are important to the functioning of society yet don't make the major news channels.