There is one thing about German highways that is very perculiar and special in all of Europe. You usually can drive as fast as your car can at its peak power. However, at the same time Germanys high ways are clogged, under funded (won't go into details on that one here) and badly controlled. There are too often sections where 100 km/h (that's about 63 miles per hour) is the limit. On top of this restrictions there are always sections that are under repair or are just clogged by all of Europe travelling through Germany.
This leads to an underestimated pattern in traffic behaviour, which is as of now not recognized in modern traffic cycles like the NEFZ (New European Driving Cycle). Usually, on all privately owned European high ways, there is a limit of about 130 km/h (about 80-90 miles / h) and you have a lot more steady traffic (which is due to modernization and pricing of highways). This leads to the assumption that on average, you are having a steady speed and thus hybrid cars are not efficient when it comes to highway driving performance.
However, I think they underestimate the amount of braking and accelerating done on a typical German highway. In my opinion there is mucht to get out of a high-end hybrid while driving on German highways at high speeds. I just made a trip from Karlsruhe to Worms, which is a 1 hour drive (under good traffic conditions) and about 100 km. Now, it took me about 2 h in reality and I had 2 traffic congestions on my way up there. Also, the lanes were pretty much clogged so it was acclerating to 160 km/h and braking down to 100 km/h about every 7-8 mins.
I'd say these are perfect conditions for using regenerative braking. On an extra note, the traffic congestions are also situations that actually beg for a hybrid drivetrain.
Now, I wouldn't consider a Prius or a BMW 1 or an A3 from Audi to be converted to a hybrid version. That'd be nonesense, because of the added weight and thus the rising consumption, but one could use upper tier cars like a Lexus or a SLK or a X3 etc.
Those cars have little to lose in terms of weight, because the extra weight is a minimal burden for them when compared with the performance return of an electric drivetrain. Also, a few thousands extra for the added hybridization is actually easier to sell with cars that cost around 70k than with cars that are in a competitive low-price segment like the Golf or an Audi A3.
I'd wager the price for a hybrid variant is about 2k to 3k (the price of an automated transmission at least) which would be up to 15 % of the price of a new Golf but only 7 % of the price of say a SLK.