Minio will always be 100% free software / open source. We have no plans to add any proprietary extensions or hold back on features for paying customers only. -- Minio Team
Then why not make the license AGPLv3-or-later, to avoid other people creating proprietary forks? I get that it's not a common occurence within the Golang world, but nothing will change unless more Golang projects start making their code copylefted.
GNU AGPL is an ideal license for free software projects. We are a strong supporter of the GNU project. We chose Apache License for Minio purely for adoption reasons. Most of our users build proprietary software around Minio and their legal council has a default NO policy towards GNU licenses. Besides, FSF has also approved Apache License v2 as a free software license.
Proprietary forks are OK with us. It will be too expensive to maintain branches of their own and catch up with the upstream.