So I also shared this on r/Steam but figured I'd share it here too since I'd like to both hear thoughts on this as well as get the idea out there. Maybe the right people will notice it. I think it'd be huge especially with what may very well set the bar for mobile PC gaming 'consoles' moving forward.

What if the Steam deck had ad-hoc LAN mode:
You meet up with some friends, but don't have Wi-Fi available, so you switch to the Ad-hoc local LAN mode and connect directly between Steam decks to play. You don't need to share a Wi-Fi source, potentially a Steam deck could host the game, and everyone could join in.

Now what if it also had a "Local Player Finder" too?
So for this, of course you would want privacy options, so consider the functionality of Airdrop on iPhones as an example. You can enable or disable visibility, as well as limiting to friends, etc.Now moving to functionality.. You're on a 4 hour plane/train/bus ride and you have a lot of time to kill. You have the local player finder enabled and suddenly you see two other Steam deck users are sharing the same ride. You send a local message, "Hey, I see you have a Steam deck! Do you have XYZ game, and if so, wanna play a few matches?"A few hours later and you've made a friend, added them on Steam, and you already have to stop and prepare for arrival.

After-thoughts:
So after talking with people, seeing the comments, etc, figured I should add a few things.
First off, can't believe I didn't consider emulators with this. That would be epic. Not to mention it'd likely give new functionality to a lot of the classic games we grew up with which were the birth of LAN parties to begin with.
Also, developers don't need to add functionality for ad-hoc LAN. Ad-hoc Wi-Fi is just a transport method for networking. Technically any game which already supports LAN (typically lets you host your own server, has a local multiplayer, or a local co-op) will support an Ad-hoc LAN if handled in SteamOS. It doesn't require any physical addition to the device, so it's essentially adding a feature (which will benefit a lot of us) for free*.

^\I say free, but yes, it does take paid working hours to add this. It doesn't take hardware or developer co-operation, though, so it's just a matter of Valve saying "Hey, this is cool. Let's add it." to make it a thing.)

This not only would benefit the Steam deck, but it would set the bar for mobile PC gaming for the future.
Additionally, this is a feature update that could be done post-launch as most Wi-Fi cards already support Ad-hoc mode, and the additional functionality could be added to Steam in regards to Steam deck usage.

Thoughts? How could it be made better? How would you use it?Feel free to discuss; I'd love to see what some of the brilliant people here come up with!