By fiddling around with the Switch it's been discovered that the lobby function is already implemented in the Switch OS, at least to some degree. It seems to be done through a web applet that makes requests to https://web-lp1.znc.srv.nintendo.net/lobby/. Looks like the name of the app will be Nintendo Switch Online Lounge. And yes, there's a typo in the logo.
Also I found the following messages on the source code of the page:
Your room has been created.
You can invite friends to the room via
the Nintendo Switch Online Lounge app.
Some additional strings:
Pass_Code
Code for friends to join the room without an invitation
Allow_Friend_To_Join
Allow Nintendo Switch friends to join the room using a code
Available_Free
You can use the pre-release version of the service for free
Service_Name
Nintendo Switch Online Lounge
Lets_Invite
Invite friends and enjoy voice chat while gaming, all via your smart device!
Need_To_Play
The Nintendo Switch Online Lounge app is required to use this feature
Send_Notification
Send Notification to My Smart Device
Join_Success
You can use voice chat from the Nintendo Switch Online Lounge app.
Create_Room_Success
Your room has been created.
The logo was extracted from https://web-lp1.znc.srv.nintendo.net/storage/icon/usEn/ico_lounge.svg. Nintendo.net is the official domain the company uses for their network (like miiverse.nintendo.net).
Look's like the app is 100% needed for lobbies and chat. Also found a QR code that links to http://lounge.nintendo.com but it's not up yet.
Edit:
Looks like Nintendo removed the pages. But I archived them anyway
https://web.archive.org/web/20170615000840/https://web-lp1.znc.srv.nintendo.net/lobby/
https://web.archive.org/web/2017061...nintendo.net/storage/icon/usEn/ico_lounge.svg