Where I work at the University of Oslo, one decision stand out as a very good one to form a long lived computer infrastructure. It is the simple one, lost by many in todays computer industry: Standardize on open network protocols and open exchange/storage formats, not applications. Applications come and go, while protocols and files tend to stay, and thus one want to make it easy to change application and vendor, while avoiding conversion costs and locking users to a specific platform or application.
This approach make it possible to replace the client applications independently of the server applications. One can even allow users to use several different applications as long as they handle the selected protocol and format. In the normal case, only one client application is recommended and users only get help if they choose to use this application, but those that want to deviate from the easy path are not blocked from doing so.
It also allow us to replace the server side without forcing the users to replace their applications, and thus allow us to select the best server implementation at any moment, when scale and resouce requirements change.
I strongly recommend standardizing - on open network protocols and open formats, but I would never recommend standardizing on a single application that do not use open network protocol or open formats.