There's one thing that a company can do if they want to prove to their users that they'll always stay open. Ask their external contributors to sign a DCO (developer certificate of origin) instead of a CLA (contributor license agreement.) The latter transfers the copyright to your contribution to the company, the former is merely an assertion that you do own that copyright and are legally allowed to contribute.

This way, all external contributors own a small part of the copyright to the project. This makes changing the license almost impossible, as it would require either seeking permission from all those contributors or removing all of the code that they wrote.

Whether a company uses a DCO or CLA should be the litmus test of how they really feel about open source. I'd strongly reconsider making your business dependent on any products from the latter.