Considering there really no big "killer" features in ST3, I'd like to propose one, which might me a big extension to ST.
Virtual File Systems API should implement file I/O based on plugins. The end developer API could be taken from existing projects, e.g. FUSE.
VFS would allow deep integration with different off-site (not local) file editing without sacrificing any time for I/O waits. While there are lots of file system wrappers (e.g. FUSE), the implementation inside ST would benefit from higher integration with text edition and navigation tasks.
There is also a number of companies which use ST in corporate environments with high security requirements (e.g. no source code should be saved to local storage). VFS capability would allow to use ST in such environments.
End users would benefit from plugins for FTP, SFTP integration with file browser.
Virtual representations would also be possible. Consider a VFS based on class hierarchy with method definitions as leaves.
All this requires minor modifications to UI, but deep modifications to I/O core.
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