ideas (you don't have to implement them all):

Private programs

bookmarked lines, and blocks

hosting files

auto save

A side pane for long programs of code

Better multi-file tabbing, and maybe folders

also the repl.it/code/number is kind of anoying, so maybe other types of version control like github, mercurial, or subversion

A menu with items like:

- File: file related items such as save, make private, download, share, settings, host

- Edit: items like undo, redo, line functions (e.g. indent, deindent, move), comment functions (comment line, comment block), code folding...

- View: editor looks e.g. theme, syntax highlighting, invisivble characters

- Settings: other settings like auto complete, tabbing, auto save...

- run: to run it

- save: (for easy access)

- Help: for help

A few more examples for each language

A desktop app for offline use, that syncs with the server when there is wifi

A bowser extension for quick code testing, (on highlighted code) and able to create new projects/files

a more codepen like way for html, css, js editing, but with having tabs

custom url slugs for example repl.it/custom/yourNameHere

a debugger that can stop through the code execution, kind of like the chrome debugger

a todo/bugs/notes (maybe integrate with waffel.io or some other service like that)

also just an idea, be able to host web apps like heroku, but using the code from a project. for example, imagine someone just has html, css, and js with no server side code,

just serve the files, but if they have some sort of config file, use the information in that to run the server file

you could also have a kind of developer console, so they could see the result of http requests to the website at a certain path. for example if the project was at repl.it/hosted/appcodeorname, and post request was sent to the path repl.it/hosted/appcodeorname.com/signin, you could show the request and response headers and body

what would be even more cool would be sub-domain support. for example repl.it/hosted/users.appcodeorname.com/userId, and if the person has their own domain, youcould host to that

a few more feature ideas from c9.io (repl.it is still better)

p.s.

in case you didn't see my other comment's p.s., i want to say that i love repl.it, and even if you don't implement all of these (I wouldn't expect you to, they are just ideas however) it is still a great editor