I'm not sure that I follow the suggestion. How would a general sign in button or page be able to direct one to shinyapps.io versus an on-premise installation of either Connect, Shiny Server or Shiny Server Pro?
From within the RStudio IDE, one needs to choose where to deploy a Shiny application. I could see it being an interesting feature request to have the ability to launch into the administration of an application from the IDE itself given that the deployment destination is known there.