you're gonna be the first...
No, I don't think it's too small - so long as you don't treat it like an 1100 and run it at 80mph all day. Take one for a ride and see what it's comfortable cruise speed is. Ask the dealer's opinion. Maybe he has a demo or last years used you could take out for a run. It will be buzzy, definitely revving at extra-legal speeds, but at legal speeds should be ok.
Perhaps you need to gear it up a tooth or two. The KLR650 for instance comes geared too low for highway, but one more tooth on the front makes a big difference.
I would definitely not plan on using it as a mainly highway bike, but as a bike you could ride a long way on backroads and gravel/dirt roads, with occasional highway jaunts.
For around the world, I think it would be great, assuming you like the backroads. That's where all the good stuff is anyway.
bikes need the rear subframe beefed-up for full luggage, especially for backroads use. If it's steel, and you can see a clear method to beef it up, go for it. OTOH, it may be hugely difficult because it's too tight a fit everywhere to add braces or support tubes. You may even have to make a new one, which isn't quite as difficult as it sounds - maybe. Some subframes are very simple, and a competent welder could make you a stronger one in an afternoon, complete with great brackets for luggage.
Share the Dream!
Seek, and ye shall find.
Inspiring, Informing and Connecting travellers since 1997!