I know having the ability to record a video track within Lumafusion isn't included and the team directs users to a more robust camera app. However, there is a targeted use for this and I think it would open up the LumaFusion app to a large community of MOBILE GAMERS that have a desire to produce their content solely on their mobile device.
Typically, mobile gamers will record a bunch of gameplay until they have captured the footage desired to cover the topic of the video. They'll edit these clips and then add in their voice over but many like to go the extra step of adding video of themselves as they speak the voiceover. This makes the video more like a live-stream in appearance and helps get more views. As it stands now, LumaFusion stops short of making this a possibility because we don't have access to recording a new video track with the built in device camera. You have all the other elements in place though ( green screen with cropping and picture in picture placement ). Adding in this last piece of the puzzle would make Lumafusion a complete package for this market. I know you might think it's a pretty limited group of users but I think a much wider audience would find uses for this feature. Product reviewers could utilize this feature as well and I'm sure a host of other users would find this beneficial.
The key to making this work is to allow the current video tracks to play as you record the new face cam track on top. There is an application out there which allows just this type of thing but it's really not aimed at people that want to create videos for posting on YouTube. It's called TouchCast Studio and it's what I am currently using in place of Lumafusion. The creators of Touchcast though aren't interested in the type of users that make videos outside of their intended use of creating interactive videos which are hosted on their servers... it can be done but you get a big ugly watermark on your video and the apps editing features are lacking.
I don't have any real hope of this feature gaining traction but maybe it makes sense to consider? Fingers are crossed