I'm afraid I haven't heard if there are plans to bring back solos or duos in the future. I know they're both something that the community has been asking about for a while now, but we don't have any updates on that at the moment.
If it is something that's brought back we'll most likely have an announcement to share with everyone. I'd recommend keeping an eye out on the Apex Legends Twitter page for announcements on future updates and new stuff coming to the game.
/Kent