1) JS is easy, almost everyone can work with it.
2) V8 is faster than LUA 5-10 times........
3) MVC - Model and crons, i think should be in DB.
Javascript strikes a nice balance between performance and high level usability.
Now cron can do directly in the database. The results you can obtain using REST request (with gzip is very less traffic). On the javascript there is a huge amount of libraries, such as Crypto, if desired, there will be templates to insert. When I finish the beta, it will be possible to write map / reduce function on the clusters. The differences will be very much.
Also, keep in mind that I wrote Lua-JIT, not Lua. There's a big performance difference between them too.