It's a weird license that seems to say "you can use this as long as you don't compete with us", with an automatic switchover to Apache 2.0 in 5 years. Definitely better than closed source, but probably not Open Source by the OSI definition.
It's actually a slightly different form of an old debate. I'm thinking in particular about the Crockford license (the MIT-like one with "The Software shall be used for Good, not Evil." bit). It was determined to be non-free quite a while back due to such restrictions.
That being said, it hard to be a commercially successful software editor with an OSS model (RethinkDB comes to mind).
I do understand why BSL exists, but it feels to me like an unsatisfactory compromise.