I'm also interested in buying the Thorn Ripio and I agree that the is weird. But things might not be quite so bad as they seem. I looked at the Ripios geometry chart and found out that the medium frame has 360 mm long seat tube. However Thorn measurements are from the centre of the BB to the centre of the top tube. I guess that the actual seat tube is about 40 mm longer. This is still a pretty small seat tube. My Orange 5 size 16 inch has about the same seat tube length and I had to buy a 400 mm Thomson seat post to be able get the right seat hight.
I'm 5’11’’ (180 cm) with relatively long legs. I used to have an 18 inch Orange Patriot mtb, but I always felt that the top tube was a little bit too long even thou I only had a 50 mm stem and 50 mm riser bars.
My long legs forces me to have the seat post high which means that the saddle comes a long way back thus increases the distance to the bars. My Orange 5 is a size 16 inch. The top tube is 582 mm.I use it with a 50 mm stem and a 19 mm riser bars and the fit is perfect.
For cycle touring I would like to have a more upright position and a longer seat tube.
The Ripio seem to be a really nice mtb touring bike but the seat tube should be a bit longer and the head tube should be a little shorter.
I hope this post was of some help
Cheers mate