Great questions - and my apologies for the delayed response...
> Also, does the submission have to be open source?... or are we able to just put binaries on a publically accessible GitHub?
The code for all of the entries must be published in a public GitHub repository, but you can license it however you wish. If there are any 3rd party (or your own) libraries / assets that you don't want to add, that's fine. I'd recommend leaving a note in the README.md file that descrives the dependencies / omissions.
> If you submit an App, does it have to be in the store?... or can ppl side-load the apk for instance?
Nope. As long as someone is able to play / download the game via the itch.io page, you're good.
> Also, who will be judging (just participants?.. sponsors?..) & how will the voting be weighed / can you vote for more than one? If you have a team, does everyone in the team get a vote?... or just one vote for the whole team? Will there be multiple rounds? How long will the judging / round(s) last? Can you make patch(es) during the judging? Will there be only one winner?... 1st, 2nd, 3rd, Honorable Mention.?. Do the winners receive anything?... (bragging rights, t-shirt, pizza?)
Everyone who submitted a game is eligible to vote. Each game will be rated on a 1-5 scale across the following categories: Overall, Gameplay, Graphics, Audio, Innovation and Theme Interpretation. Everyone on the team can vote. No multiple rounds. Voting ends on Dec 22nd at 13:37 PT. No patches allowed during the judging period to the itch.io page*, but you're welcome to push changes to the repository (as the code isn't being judged). There will be winners across all categories. There are no official prizes for the Game Off.
* if there's a bug that seriously affects people being able to play the entries that is a "quick fix", I've permitted those in the past. Just leave a note of what was changed and why in the itch.io page.
> Also, with regards to the [Theme Interpretation] judging category, am I missing something, or of the 44 submissions only like 4-6 deal with the [Hybrid] theme.?. Are the ppl submitting just going to take a loss in the [Theme Interpretation] judging category.?.
That's quite possible. The entry pages should have a sentence or two from the creators about how they interpreted the theme.