I don't know that it's at all clear how successful Terraform would be if it started with a more restrictive license. I mean there is a reason why a lot of projects start out with a different license and only change to BSL once a certain level of popularity is achieved, right?
As a possible contributor, and with all things being equal (which, really, never happens), I'd prefer a GPL-based product to have my time over a BSD/MIT license, because I really want my work to remain free. A BSL-based product would have to be very important to me to make it worth for me to dedicate time to it.
In reality, the usefulness of the product and friendliness towards developers is much more important.
