Maybe a possible feature. Was wondering if it would be possible to keep mirror up while toggling the switch between photo and movie mode(eos 100D for instance)? As for now switching modes will release and close the mirror causing an extra step opening the mirror again. Usage could be focusing capabilities in photo mode while idle and then switch back into movie mode for filming for instance.
Interesting idea. Maybe something that holds the mirror in the raised position?
I've been thinking about behind the lens filtration and the commercial versions I looked at physically hold the mirror in the raised position.
(https://live.staticflickr.com/65535/48214312017_4dc59e1cfa_n.jpg) (https://flic.kr/p/2gswXcF)
There are several benefits to using a filter behind the lens instead of in front of the lens, like being able to filter wide angle lenses that don't have filter threads and the light bouncing off of glass filters is less of a problem. Back in the days when view cameras were a staple of professional photographers placing the filter behind the lens was very common.
The VAF filters (http://www.mosaicengineering.com/products/vaf/faq.html) that reduces aliasing on DSLR cameras when shooting video are placed behind the lens as are some light pollution filters for astrophotography (https://fstoppers.com/gear/review-astrophotography-filter-deletes-light-pollution-full-frame-cameras-167266). There is also a behind the lens filter holder for Arri cameras (https://www.fdtimes.com/2012/11/23/clairmont-alexa-in-camera-filter-system/). In any case putting a filter behind the lens is still a thing.
By the way, what I'm thinking about experimenting with is behind the lens net filters--basically using women's hosiery to soften the image. This trick goes way back and it is still being used today though the implementation is usually very low tech (http://theblackandblue.com/2013/12/17/how-to-net-cinema-lens/). What I've been pondering is a 3D printable filter holder, that would be cool.