[Markismus]

Javascript&Python support:
The frontend is entire coded in lua. If you want to use javascript or python code you'll have to google for libraries, e.g. lunatic-python. So basically: no support! Do not expect pull requests not coded in lua to be accepted. I remember some conversations about it in the past and the the consensus was: Lua only.

Editing:
Before we can edit epubs, koreader will need a text editor. For now, there isn't even a note editor written. I would love that feature! Adding an epub editor than only requires the epub to be decompressed somewhere, edited and recompressed. The big problem for a note editor seems to be the lag in displaying typed text on screen and people willing to implement it.
These editor features should be hacked into the frontend as plug-ins, so that people like Ken don't have to enable them, if they don't want to use it.
If you want to edit text/code-files and are using a Kobo device, you could look at KoboLauncher which does include an editor.

Use telnet access:
Koreader now has a terminal simulator that generates output for a given command. This simulator would need a fairly big overhaul to allow for vim editing. I think for something that involved, you would be far better of by enabling telnet or USBnet on your device and using your mobile phone or PC to access your reader: You'll have full terminal support, including vim or whatever editor you like to install.

Keyboard:
You really need to differentiate between a device and the installed software. No, the software does not allow you to magically attach a keyboard. However, the linux installation on for instance my Kobo Aura H2O can be hacked to allow it. IIRC, the frontend detects whether there is a keyboard attached on startup and adds keyboard shortcuts to the interface. This feature is normally only used when you're hacking the frontend on your PC.