I was not aware that you could sign up for 5e D&D games with particular companies? Is there a parallel or shadow registration process outside of the Gen Con Events registration? If so, where?
Thank you for the tip about monitoring other games for available slots. Is that something you do online or by milling around where lots of other games are being run?
What is the games library? Where is it? And how does it work?
I think there are limits to what Gencon can do. Who wants to go to Gencon to volunteer to be a backup and potentially do nothing for blocks of hours 'just in case' and potentially never use whatever they designed or worked on. I'd rather just find something else to do in a case like that rather than just have a GM inserted that might not even be remotely prepared.
The games library is board game centric not RPG related.
You can always search for games online. to find a new one.
Search "Games Library" for tickets to it. It is boardgame centric and you check them out or join a group. If sold out you can usually get in with Generic Tickets.
There is also FEPH First Exposure PLaytest Hall. https://www.gencon.com/gen-con-indy/first-exposure-playtest-hall-feph
Open Gaming is also available in the Marriott.
And you will probably find that you have not put enough time aside for the Exhibit Hall....
Mike
Regarding the Games Library, while I don't dislike boardgames, I'm not a big fan of them either. Knowing that there is a Games Library is no doubt useful for some reading this thread, but it's not a solution for everyone.
What I am getting from this is that you want to play as much RPG, specifically 5th edition D&D, as possible. It looks like there are still hundreds of 5th edition D&D games with open slots. If a Thursday 8AM game in the stadium was cancelled, at the moment there are 3 others in the stadium with open slots. That's the kind of thing I was talking about, but checking day of/right before you would potentially need the slot so you would have a close by backup.
Also, consider overbooking yourself to the point where you will end up being happy if one gets cancelled, because you wanted a chance to go to the dealer hall/eat/etc. [This is not what I would normally recommend, but you seem to be really focused].
Do you DM at all? It seems like perhaps working up a D&D 5th edition one shot and heading over to open gaming at the Marriott might also be a decent backup for you.
I have to be honest, I have a hard time visualizing who GenCon would recruit to act as a volunteer "backup DM". You'd need someone who is A) ready, willing and able to go all the way to GenCon and run a game for a group of strangers, but is also B) willing to sit in a bullpen to possibly play their game with a group of people who literally would rather be doing something else instead of getting a proper slot with a proper player group who have actual buy-in.
If they're in it for the pleasure of the game, why wouldn't they just run it on their own?
If they're trying to rack up event host hours for compensation purposes, why wouldn't they take the more sure deal of scheduling their own block versus risking reduced compensation if they block out their time and don't get called up?
If they're hoping to get a bunch of "easy money" (in whatever form the Con would reward backup duty) by volunteering to cover a slot while actually hoping they don't get called, do you even want to be stuck in that person's game?