I seriously doubt that it would work without any changes. X2go depends on a
lot of X specific black magic, amongst others are nxproxy, which is a way
to compress the X protocol. Android does not run X (as far as I know), so

Android has had X for some time now:
https://play.google.com/store/apps/details?id=au.com.darkside.XServer&hl=en


nxproxy is not yet there as far as I know.
Yes, it might be a lot of work, but a worthy one: lots and lots of devices come with Android.
I have wished so many times that I could use it over Android to control my servers.

@Mike:

Isn't there a functionality that lets you run an quasi app on a webserver that then allows you to use a browser to emulate an X2goclient?
I have heard that you did such functionality and that it is finished. That would be the solution: just run a apache webserver and then on Android connect to the webserver with a browser and use X2goclient like this.


 
you would run into problems there already. Next up would be code to control
when to show an on-screen keyboard, and translating touches on the screen

A hardware keyboard would be a must (bluetooth), as otherwise you will lose all screen real estate to the keyboard. But talking about Android also means Tablets and on a 10 inch Tablet, X2go would be a totally wonderful thing to use.
Considering how many devices exist that run Android, the "market" would be huge. You may even be able to charge for the app (like 1 or 2 dollars) as the X2goserver is already free and totally amazing to use. Often, Android users are convenience users, lazier than PC or Laptop users and will preferably shell out some cash before looking around for a free alternative that needs more work.
And I would definitely buy it for 1 or 2 dollars, it would be well worth it.

(providing a free trial version that is limited to 5 minutes for a session so people can try it out would work great)
 
to mouse input. To sum it up, I think it would require a lot of work to get
x2go to an even remotely usable state on Android.

You can also connect a mouse to an Android tablet/smartphone by the way. My Gingerbread (2.3) Ice cream Sandwich (4.0) and Jelly Bean (4.2) Android all supported plugging in a mouse and keyboard via USB connector, it just treats it as HID, and simulates it, so you can use the cursor keys to more from app icon to app icon or ESC to go back, as well as getting a mouse pointer to click on stuff. I was amazed how dynamic this works.

Anyway, for the short term, the webserver solution should work easier. 
 
Regards,

Markus