I have used Sublime for about a week now. I enjoy it for the most part.
Pro: nice layout, flexible key bindings, package control, REPL, multiple themes, autocomplete, matching brackets, matching quotes.
Con: install packages some packages require github and terminal knowledge. Even some good packages don't have well-written manuals. key binding is written in JSON, you need to understand JSON. REPL is great, but needs some more work.
Overall: Sublime is my favorite. It would be nice if is better integrated with point-and-click and drop-down menus. For example, you need to browse package codes to make changes, not everything is in Preferences.
With that said, RStudio IDE is a successful open source IDE, they are doing well. SAS is proprietary software, and it is not. Octave is an open source, IMO not doing well. Matlab is proprietary, and it is doing well. So, it all depends on where the leadership of the team takes it.