I agree with Maniack and Aleks.
If Yunohost integrates non-free apps, it’s like we promote non-free softwares (and that’s not the goal of Yunohost at all). For the license part, I don’t think it’s really ok to integrate proprietary software (moreover for most of them you have to agree with a EULA or something like that) and for some other, you can’t distribute code as you want.
Just for information, if a problem happened and that the app is in Yunohost-Apps orga, it’s Yunohost which will have problem and the person who maintain it… so I’m not sure we want to take the risk.
Then, there is a confusion between Free = no money and free software which have a philosophy and an “ethical” part that we may lose in integrating Non-free Software.