I am a freelancer and recently, built software for an organization. Our deal was for me to develop and submit software at whole. Hence, it is a proprietary software owned by that organization.
I've got a few many ideas about new features and upgrades that can be integrated into that software. But, the organization is not interested in any upgrades.
Being a beginner, I want to do it anyways to flaunt on my profile & maybe to sell to some other organization if I don't make the upgrade open source.
Is it ethical for me to do so? Also, what legal complications might I lead myself into?
P.S.: No legal documents have been exchanged between me and the organization. Everything is just verbal. & they may or may not have a license for the software I submitted...