there is never even an opportunity to submit design work.
nowadays, design work is code (or at least markup). Like .qml or .glade or even html/css.
is asking people who don't typically code to do so
encounter a problem and learning a new tool to solve it, is a pretty standard situation in IT. Designers have varying capabilities in that domain. While a print designer might have trouble learning a new software, a MMI-Architect or UI Designer should commonly be able to learn a new UI framework (designer software).
Generally, if you like to contribute to any project (not limited to software), you can't expect the project to adapt to your toolset.
But often it's enough to share an idea for it to get adapted.
you can start by opening an issue, sharing your idea, uploading drafts etc. like I mentioned.
because what you wish contributing to is a technical matter. You can't modify airplane design without a single clue on aerodynamics. Same with software.