Other stocks do it. When you upload MOV file they reencode by themseft automatically and sell different resolution for different price. Based on actual videohive prices. it may looks like if author upload 4K file which is usually priced for $30, then system let customers to download Full HD for $5, HD for $4, SD or $3. I don’t know if anybody need this. It make sence to downsize to Full HD from 3-4K. But I don’t see reasons to downsize further to save customer $1 of already cheap item. And automatic downscale will intruduce additional encoding which is bad for quality.
Better feature would be optional automatic preview generating for footage like other stocks do.
Best Regards, Andrey