I worked on some systems that supported Riak as a deployment option in 2013, but haven't since.
There isn't much recent news on it: https://aphyr.com/posts/285-jepsen-riak is from 2013 and Aphyr hasn't written about it in years. Armchair suspicion since we haven't heard about it in years is that it's pretty much end-of-life, deployed in a few legacy sites. But I'm curious too if it's still being considered for modern infra.