Looks like something I would have really enjoyed, but Sofia maybe not so much. Having missed those kinds of roads I still think I saw pretty ones riding up through Wales, although maybe more mainstream ones.
I had a ride on a cannondale a while ago. The only electric mtb I rode, it’s astonishing how a properly assisted bike rides over any terrain and climbs doing 20 to 25kmh with minimum effort. Assuming they have developed batteries over the last few years you’ll be onto a treat.