Needed for 0.5 (i.e. "semi-public" release):

+ hard-abort - different process handling so you can abort anything with C-g
+ good erlang shell
- get slang's default colours under control

Still needed for respectable 1.0:

- buffer modified/unmodified flag
- handle sigwinch
+ completions
- window config save/restore for popups (e.g. after completion)
- stabilize API - get rid of export_all's
- some sort of "panic" procedure to ensure that crashes don't lose data
- robustify: commands making bad calls to buffers shouldn't crash the editor!
+ M-x
+ be group_leader in Erlang Interaction mode, in some sensible way.
- integrate with normal erlang shell

For future versions:

- colours / syntax highlighting
+ erlang programming mode
- documentation browser - wiki-mode instead of texinfo?
- isearch

Things that it's really bothering me off not to have:

- fill-paragraph
+ search
- isearch
+ M-x
+ C-x 1
+ auto-mode-alist
+ tabs: count them properly for column-wise stuff (goal column)
+ find-file opens relative to current buffer
+ completions
+ contextual history in minibuffer
- parenthesis matching
- line numbers