Usual disclaimer: these opinions are my own, not likely to be those of others at ECC, etc.
I’ll just very briefly add my position here: I am a fan of copyleft licenses, and I believe that Orchard should be dual-licensed under BOSL/GPLv3. As the GPL is a more restrictive license than BOSL (it requires immediate release of source code with a binary, rather than a 1-year buffer) this increases the usability of Orchard within the free software ecosystem, while still allowing closed-source use with the “1 year head start” that BOSL provides.
Copyleft licenses explicitly defend against private capture of public goods. And I wanted to respond here to something that @secparam suggested - that BOSL is intended to be a “try before you buy” license. I personally don’t believe that this is the intent of the license. As I understand it, when a third party creates a derived work from BOSL-licensed software, they are compelled to provide the source under the same conditions after one year. This means that if, on day 1, I make a modification to BOSL-licensed software, those modifications must be released under BOSL on day 366. However, consider what happens to the modifications that I make on day 2: those must be released on day 367. This creates what one could consider a “sliding window” of proprietary advantage: a company making BOSL-licensed software gets a perennial 1-year head start on competitors that want to take advantage of their improvements, but the important part is that those improvements eventually become usable by the commons. Software evolves quickly, and a sliding 1-year head start is sufficient to obtain a profitable first-mover advantage, without requiring closed-source software.
In a way, this is kind of the same idea implemented by patents and copyright ownership in general: an entity gets time-limited exclusive rights to their improvements, which must eventually be shared with the commons. It’s the duration of copyright and patent terms that makes them abusive; a 1-year exclusive right seems like a better balance for software, to me.