If this would be an option for some other tournament, something new, something like a friendly cup I might agree but like you said no.

1. Players can abuse, play only in CUP for exemple, over and over again.
2. Is far away from real football.
3. It's gonna be a pain in the ass for T11 when they will have to prepare teams at the start of the new season for CUP/CL/League.
4. After some level is already hard to find players for the new leagues and like this would be even harder.

Cheers!