When I was fixing bikes for the local MSF I worked on a few. If any small bike is a mini-ADV bike, that is it. Not sure, past adding farkles, what I could do to improve it.
Not sure it needs that much improvement, but if i was contemplating such a thing as a small compact ADV bike, it would be IMO a sound base .
My thoughts would be Look into as in research any inherent weakness in the stock bike, Such as say for example, ( if TW200s are abused/ overloaded or brutaly used ) do they have any Frame cracking or areas that could be improved?
Loosing weight is always a good thing, and perhaps removing factory items replacing with improved or lighter stronger or simpler parts or components, rear shock perhaps.
Being an ADV bike, could you say design a panier rack frame, that though adding a little weight perhaps. some if not all of that weight could Brace up the rear subframe area (if it is needed of course).
The Wheels? Relacing up lighter stronger rims etc, lighting mods or seat allteration or replacement, or any fuel range improvements as in tank swaps or perhaps planing and fabricating an auxiliary fuel tank / cell .
Remove or Reposition any stock items Battery box air box( Obviously the latter with careful consideration of effective fueling issues such a move could make, and if its practical worthwhile or even possible to remove or change the air box).
Laboring a point here perhaps, but i see a kind of thinking mans build, rather than a typical farkle adding exercise, if you get my drift.
so many projects you see are missed opportunities to acctualy turn a bike into a genuine improved example of the factory offering, that was built down to a price rather than a high specification.
I have long since hankered after building my own Giant TW600 Bassed on my beloved and here till i die XT600e.
Hang on i just made an alternative build suggestion, that or a TW ued XT250 / 350.