I can't see why the Yamaha 125 not suitable for long distance touring. If you ride it and respect it's limits, meaning you don't ride with the rpm near redline all the time, it should be fine. Do the maintenance according to schedule and it should be ok for a 30k trip to Europe. TokyoKid did that with his wife. That's 33k Km from Shanghai to Berlin.
I've had the same questions about the Shineray VS Yamaha and eventually got the Shineray GY-7. I've put 10k on it so far and no problems so far.
But for a long trip like yours the bike needs some mods before you set off. This is not an exhaustive list, but here's were I would start: 1) Chain, front and rear sprocket. The bike is geared way too low stock, hope you won't have as much truoble as I did trying to get replacements. 2) Seat. It's a really shitty seat, I bought a replacement from Jialing and it's not much better either. Unless you weigh 50kg, you'll find the foam way too soft and it will be painful. 3) Tires. The bike will feel much better with better DS profile tires.
Any bike would be ok for long distance touring, so long as you ride it within it's limits and do the proper maintenance. The Shineray won't be ready out of the box as the Yamaha, but it will take do better off-road, where all the fun is.
Hope this helps.