@IDA_ML
Not sure how it is on the 100d, but I guess it's the same as on the 6d.
With 2688 x 1166 at 25 fps I have real-time live view (but indeed with 5x zoom, so not exactly WySiWyG, but at least centered.)
BUT if I do a half shutter press and hold it that way, I see the ML preview pop up on screen, which gives a WySiWyG framing, but the ML_preview is not that high in resolution and it's not real time fps but slower.
Once I have framed my shot, I quit half shutter press, and press record button.
When keeping the ML preview while recording it's slows down the camera which results in shorter recording times.
With the higher resolution crop_presets I have scrambled live view, but I can let normal ML_preview pop up with half shutter press.
It's this option in Raw video menu
(Be sure that global draw is set to'ON all modes' in the overlay tab menu):

You could also choose for the option 'framing', that way it automatically does ML preview, so no need to hold half shutter press. but as said before, expect shorter recording times when ML_preview is used while recording.
About recording times on the 6d.
I found recently out that in video mode it does about 60 to 62 MB/s write speed(with SD_UHS hack). (always thought it was 70MB/s just as the benchmark in photo mode shows)
With 2688 x 1066 at 25 fps I get about 6 to 7 seconds of recording time.
But I'm planning to use that mode with 2560 x 1072 at 25 fps (1:2.39 aspect ratio)
That way I get 9 to 10 seconds recording time with 14 bit lossless and SD_UHS hack.
Would be cool if lower lossless bitrates could be fixed again.
Have tried to fix it with using the analog gain registers, which works, but the problem is it also affects the ML_preview. So not really usable for 10 bits lossless, image preview get's really dark

.
Furthermore I couldn't fix the white level in camera, so has to be fixed in post proces.
I think the way to go is using the analog gain registers, but altering the crop_rec module to only enabling them while recording. Which is way out of my league for programming, just as fixing the whitelevels correct in camera.