It's not only considered, it's a an actual goal to be 100% usable by everyone. It's already the case for some of La Suite projects. Not quite there yet right now for some others, but it will be.

And I agree, lots of popular, proprietary solutions should do better in terms of accessibility. I believe open-source helps in that regard, as in many others.

Here in La Suite we have some wcag-geeks in the team and regularly include some of our users with disabilities for feedback.