I actually think that it's a social and business problem, more than a technical one. Some SaaS providers already choose to run an OSS product which they develo

I actually think that it's a social and business problem, more than a technical one. Some SaaS providers already choose to run an OSS product which they develop for their needs but also share (like GitLab, Discourse and Sentry). Others choose not to publish their code, and lock the software to their infrastructure. These are business strategies as well as ethical decisions. Different technologies might change the cost/benefit ratio, but people that really want to be OSS already are.