It's a very nice design, and it's the most affordable digital rangefinder camera in a market that is saturating rather slowly. That keeps the price up. The DSLR and mirrorless markets are saturated. There are many good cameras that you can only get some change for, and new models are coming out as I write this short post.
The only real issue with R-D1 is the sensor performance which is really starting to fall behind from the practical point of view. I don't mean this so much in terms of image quality, 6 MP continues to be plenty for many (most?) applications provided you frame it well. And while this is no high-ISO monster, it is quite usable where there is some light (a nice concept for photography anyway). But it is 6 MP with a severe crop and too much vignetting vs. what, say, Sony has out these days. While Sony has performance issues with wide M mount lenses, the Epson was always a bit limited in sensor performance, too. The only new lens that upgraded the Epson performance is the Voigtländer 21/1.8. And it's a very moderate wide angle on R-D1 with no framelines.
The R-D1 is a beautiful camera that deserves an updated sensor and more viewfinder options. Looking at what the market offers, this camera still offers what makes sense for many of us. I think very few people who have spent years with this camera would disagree.