Nintendo have recently updated information on their Nintendo Switch Online website. When the Subscription service finally goes online, twenty NES games will be available to play online with friends. You will also have the option to voice chat via the Nintendo Switch Online app.
Here is an excerpt from the Nintendo Switch Online website:
With online play added to every classic game, you can compete (or cooperate) online with friends, share your screen, or pass the controller, depending on the game. With the Nintendo Switch Online smartphone app, you can also voice chat during your play sessions.
As mentioned before, 20 NES games will be available from launch of the paid Nintendo Switch Online service. These games include Donkey Kong, Super Mario Bros, Balloon Fight, The Legend Of Zelda Ice Climber and more.