Any ideas how? 

you have just to find 2000mm profil and 2000mm leadscrew and yes it's possible ^^

But I don't think that the x-axis will be stiff enough to be 2 mheter, without any added support.

the X axis is very rigid, I think i can handle 2000mm pretty easy

One of my instagram followers made the TopsCNC Heavy Nema 23 with 2000mm for X and 2000mm for Y, and  the machine seem to work pretty well ;)

@Carsten: to complete @Topsie's answer: you can go easily to 2000mm x 2000mm, and if you have any issue, it's more probable to be in Y-axis than X-axis!

For X-axis, for top rigidity, if you can buy 2x 2060 and 1x 2080 instead of 5x 2040. I've (and others too) made this, and it will improve a little bit the rigidity (and in my case, these 3 extrusions was also cheaper than 5x 2040).

I've done a 1500x1500mm TopsCNC Heavy and no problem so far, and using Nema17! But if you go bigger, i will definitely recommend Nema23 and bigger leadscrew than T8 (T10 or T12)! 

Good luck! ;) 

Thx.  DavidC

Any ideas for the Y-Axis i 2000mm ør longer? 

DavidC. I went the same route, 2-20x60 and 1-20x80. Carsten at a minimum Iwould increase the amount of Y axis braces double the length use 4 braces. The issue I think you will have when you go to 2m is deflection on hard X axis movements. 

@Carsten, if you go longer than 2000mm, I think you need to know if the TopsCNC project is suitable for your needs. You need to consider the speed of the overall machine, are the 3D printed parts made to hold such stressfull operations, etc... I agree with @Peter Donovan.

If you still want to go with TopsCNC for more than 2000mm axis, I think the Y-Axis should be redesigned to use 2080, or C-beam profiles, to improve the rigidity, and many printed parts should be redesigned.