First, I think you're doing a great job. Now, let me whine about your product a moment. :)
My support staff is a group of non-technical people, so I would like to avoid having to teach them the skill of manually adding params in an html editor, if possible.
I understand your goal is to support more than just YouTube videos, so I can also understand if this isn't something you want to do, but if it could be an option, I'd like to see (at minimum) width and height param inputs on the 'Insert Video' form.