Elastic Beanstalk

Many Elastic Beanstalk environments to be retired on March 1, 2020, with additionally Windows Server 2008 R2 to be retired earlier on October 16, 2019

It's unclear what these retirements really mean, with the statement "Elastic Beanstalk may need to automatically remove the Elastic Beanstalk components and transfer ongoing management and support responsibility of the running application and associated AWS resources to the customer."

https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/platforms-support-policy.html

CloudHSM Classic

Gemalto Luna 5 HSM's will be terminated on April 1, 2020

https://aws.amazon.com/cloudhsm/faqs-classic/

Lambda execution environment

The underlying Amazon Linux will be updated for all existing Lambdas on June 11, and May 21 for newly created Lambdas.
https://aws.amazon.com/blogs/compute/upcoming-updates-to-the-aws-lambda-execution-environment/

S3 path back-pedal

AWS changed their plan for the S3 path change, to allow buckets created before September 30, 2020 to continue functioning as usual. Only buckets created after that date will be impacted. See the blog post https://aws.amazon.com/blogs/aws/amazon-s3-path-deprecation-plan-the-rest-of-the-story/