Why? You can use it to develop apps without any restrictions.

I would offer a commercial licence for a fee. It should come with some level of support, and use this to fund further development.

Corp lawyers have said no GPLv3 for tools like this before

Unless the engineer in question isn't responding to emails, then your company can use the same strategy with GPLv3 code as they would with any propriety code: Pay for a license.

Or does your company not use any propriety tools at all? (It's alright if they don't; being 100% reliant on permissive open-source licenses is a nice achievement in-and-of-itself).