@johnmn
Please find below the reason for why R is not supported?
R is currently not supported in Shared clusters due to the specific limitations and configurations of these clusters. However, Databricks has recognized this gap and has plans to support R workloads on Shared clusters in the future. The timeline for this support is not yet defined.
We are not dropping R support, and R will be supported on Shared clusters as well.
We do have a feature request raised for this: DB-I-7350