FWIW I downloaded the source clip and converted it to double fps using 3 different settings:
The first conversion was plain jm_fps using default settings.
The second one used mx_fps (a mod of FrameRateConverter by MysteryX which adds artifact masking). I also used "DCT=1".
The third one also used mx_fps, but I also changed the default block size of 16 to 32.
Download here:
https://www.zeta-uploader.com/40449651
A few remarks about the source:
It seems to come from the Apple world, I had some problems to convert the VFR video to CFR without loosing audio sync. All my AviSynth source filters failed, only FFmpeg could do it. I needed to convert the HD source to SD, my slow computer does not like HD...
All the conversion results cannot handle the snow flakes, but at least to my eyes they all look pretty good. This is probably all you can get from MVTools based interpolators.
Cheers
manolito