Microsoft recently announced a full language server for VSCode. Whilst I'm not the biggest fan of VSCode I think there could definitely be some features that could be "borrowed" somehow to make markdown editing even better.
Features include:
Document outlines
Workspace symbols
Document links
Smart folding
Smart selection
Completions
Rename
Find All References
Go to Definition
Diagnostics for broken links
Updating of links on file moves / renames