highway is possible I think, but you'd have to get some major stuff done to improve it before going there.
Highways and Interstates are definately doable on a stock bike, no question. It's just a matter of how long any particular person can put up with it both mentally and physically. Some people don't seem to have any problem busting ass for 4-5 hours at 80+ on a stocker..... NOT ME!!
There isn't much the KLR can't do and that's it's appeal, but most of everthing it can do is based on rider ability and their willingness to do so. Like the highspeed interstate runs for hours and hours, or extreme offroad hills, or extreme curvy roads at faster speeds. It's not a full blown sport bike, cruiser, tourer, or dirtbike, but it does have a little bit of all of these abilities in it.
Goldwings and big tourers aren't exactly curve dwellers at speed and definately won't be hitting any dirt trails. Although I've seen video proof of the new goldwing being flicked around like it's 600cc sport bike on deals gap, this is simply not the case for your average rider.
Sport bikes don't care for interstates much and they won't be hitting any dirt. I did a 200 mile interstate run on a sport bike back when I was 20ish and would never do that again, just had no appeal and not a comfortable riding position for extended periods of straight line runs.
Cruisers aren't the best interstate bikes in stock form either. They won't be seeing any dirt and don't exactly like twisty roads at faster paces either.
But the KLR.... even beginners can enjoy spirited runs in the twisties, it will do interstates for some random period of time, it loves 2-lane 50/60mph highways and will go just about anywhere off-road, especially if you are riding in a group where some assistance could be helpfull here and there. It will do it all on demand even though it may not do it all perfectly.
Where I live, it's a tough battle for me to want to keep the KLR. One day I'm ready to sell it, the next day I realize it's an amazing all around bike. Plus, the bike I want (Concours 14) is $13,000. I found some places to ride around here, but the few other KLR riders I know in town never ride. So I'm always way to cautious to have much fun on these trails. Plus, they aren't exactly LBL quality or length. Like I said.. it's a battle!