I'm just curious whether companies are open for this. Lately there is more traction towards open-source and whether a person can start contributing to it and later join the core team.

one personal example i've read is the developer of nomad levant project was acquihired[1] by hashicorp

[0] - https://github.com/hashicorp/levant [1] - https://twitter.com/jrasell/status/1230132251893125120