Nam, your bike needs ground clearance and more suspension travel - there must be easier ways to cope with that apart from Rally Raid huge $$$ - having said that, you'd also need a longer side stand. I'm not sure that I'd bother with an expensive 19/17 conversion as that won't get you the narrow width rims required for off road (unless you go with a custom spoked set) and at that point, you'll just crave the front 21" for its narrow width, huge choice of tires and the rolling ease associated with the larger diameter front wheel. I find the going to a 19" and having to use a 110 tire up front won't offer you much more than your current 17" with a 120 front tire - soend your money on a new KTM 500EXC 6 Days edition
As for anyone running 19/17 wheels on their bikes and if you're looking at TKC80s, they're extremely good tires and last a decent amount of time/use on normal bikes but the KTM 1190 adventure literally eats those things up given the power and weight - expect no more than 3500km for the rears. I ran Metzler Karoo 3s on my 1190 adventure and same thing - eaten up in 3500km of mixed road and gravel. This may not seem too bad to some people until you look at the price tag but Shinko offers an amazing alternative (continental manufacturers some of the Shinko tires).
Look at these bad-boys:
http://www.petes-superbike.com/sr804805-extreme-dual-sport-c-2234_1_4368_6828.html
The pricing is literally half (if not even less) than a TKC80 and they are almost identical in pattern and apparently the same exact construction and compound. Kenda offers their Big Block adventure tire in similar (actually more) price range but I've heard that they're deadly on wet tarmac.