MLBTR just posted a good breakdown of all the recent pre-arb extensions:
https://www.mlbtraderumors.com/2018/01/extension-records-pre-arbitration.html
A Swanson extension isn't likely due to his struggles, but Albies and Acuna are candidates.
The record extension for a player with less than 1 year of service time is Anderson's 6/25 deal with 2 options ($12.5M and $14M). A similar deal with Albies would guarantee his age 21-26 season, and give the Braves options over his age 27 and 28 seasons. This is a deal I think the Braves should strongly consider, especially if they can use some funds from this year as a signing bonus that covers a chunk of the overall deal.
The record extension for a player with no service time is $10M to Singleton. The Astros essentially guaranteed Singleton $10M over his pre-arb years and first arb year in exchange for 1 FA year option. The deal was signed the moment Singleton was promoted after the Super 2 cutoff. Would a similar deal make sense for Acuna? Should the Braves guarantee him ~$10M through age 24 in exchange for a ~$15M option over his age 27 season? It seems like Acuna might be a good enough prospect to gamble $10M with the hopes of tripling that money in surplus value when he is 27.