I would gladly support auditing Keychain, we are usually posting very frequent updates, which would make repeated external audits very expensive.
After reading the comments section, I do have a few remarks and questions though:
The project started small and grew fast, and that led me to decide to start a refactor a few months back, that will hopefully be ready by year end. We are rewriting the entire code base using React.js, is it a library you are comfortable with? Also, this means that depending on when you start, you'd have to review the entire code twice.
Yes, Keychain Mobile is 100% open source: https://github.com/stoodkev/hive-keychain-mobile
I would also like to see the question of your credentials being addressed. Not that I don't trust you have to skills to do this, as you put it, you've built a reputation here. However our ecosystem is growing faster than ever and your reputation won't mean much to new comers. Could you include a list of relevant projects that you've reviewed/audited in your proposal?