Hey! I'm working on my custom engine with a custom lisp as scripting language. I would love to join the jam to challenge my engine, but I'm hesitant about open sourcing it. Mainly since it'd take a lot of work to take it to an acceptable state, now it's just a bunch of smoke and mirrors tied together with duct tape... Is open sourcing everything really a must?

I don’t think it would be appropriate to make an exception to the rules for this.

The rule is not that the engine has to be open source “in an acceptable state”; just that it’s open source. You can worry about polishing it later.