In iMIS15 since logging into iMIS is server side you can not specify which database to login based on associated iMIS libraries. This makes it so it is easier to by mistake log into the wrong instance of a customer's setup.
When using RDS this is not done on a per user bases. This means that iMIS users accessing the Desktop to access instance A will change the default database being logged into for others.
This is going to have a big affect on hosted clients
For hosted clients this is going to be a big affect if you host on shared servers. Even using Citrix this will be an issue.