Sebastian (MacBig) is the only one that I am aware of that is using the VM28, and his bike is not a stock TW200.
He has posted that it is not a easy carb to get properly tuned.
Perhaps he will soon post about it.
An alternative carb is one of the Chinese copies of of the Mikuni VM24/26, listed on eBay as a BW200 carb.
The carb will work (I have tried one on my TW). However, you will need to modify the carb screw-on top, where the throttle cable connects.
Or better yet, make a custom throttle cable, so you don't need to mod the carb top.
Either way you will need a different cable, and perhaps a different throttle control. The stock throttle cables are in a push-pull configuration, and the VM28 is a single pull cable, which has a different lug on the carb end.
The Chinese carb is also shorter from front to back so the air box boot is too short. Another forum member has solved the problem using duct tape.
If you bike is a pre-2001, you will also need a separate start/kill switch.