You can also go to repl.it/languages and see all the langauges.
As for our plans to become an IDE: we've given ourselves the hard task of being a REPL-first IDE and to always load in under 2 seconds. More here: https://repl.it/blog/platform
For the landing page: we've found that most people coming through there go through the signup/login flow anyways so we've emphasized that. You can still get to the languages in the footer.
This baffles me. Why? Don't people just want to mash something into a REPL quickly (step in between: write the first one or two letters of the language you want to use and press enter)? That's certainly how I use it ...
We also just discussed this and we're adding a language selector on the homepage.