I'm a developer who makes open-source software, typically libraries and websites.
My libraries are under the Apache 2.0 license, while websites / applications are under the GPL/AGPL 3 license.
I've been reading into copyright and licensing and understand that contributors retain copyright of their contributions, and that if I hypothetically wanted to change the license later, I'd need the consent of all copyright holders (contributors) to do so.
I have no qualms with this, but I've been wondering if it's practical to provide the means for individuals to voluntarily sign an optional Contributor License Agreement (CLA). The goal is to minimize friction to contributing initially, but to also encourage signing to reduce potential headache should I ever want to change the license, or update to a later version of the current license.
This seems optimal to me, as it grants contributors the choice to grant the right to relicense, while not obligating them to do so just to contribute to the project. However, I've failed to find any projects that do this.