I'm not saying it'd be easy, or that it'd scale to a massive company, but then I don't think we should have such massive companies which is another discussion.
The examples you give are more like every employee getting to decide what they feel like working on. The idea would be for employees, as the ones almost always closest to customers, to define what they see as mattering most.
You have to remember that OKRs aren't just tasks. Ideas from the bottom up would include what they see as most important along with why its important and how success will be measured.
All of the examples you gave could be great examples if they are complete. Publish more open source to break into a new market or improve code maintainability. Migrate to a new library to fix long standing performance issues or unlock a new feature set. Redactor for readability to reduce code review time or speed up new feature development.
Other, more customer focused, examples could be to improve docs to reduce customer churn or improve discoverability for new users. Maybe you help in a support channel on Slack or Discord and find a ton of users asking for some specific integration, its very easy for you to see that pattern but hard for someone at the top to see it or assign it value.
Pushing down orders from the top is easier, and better at stoking ego. Hiring and developing your team well so you can honestly take their recommendations and craft the next 6 months of marketing or define a new product direction that ties together what your team has seen is much, much harder but an amazing strategy if done right IMO.