I'm an ex-GS1200 rider who has switched to the Multi 1200. I loved my GS and hung on to it (it was an '04 model) waiting for BM to bring out a version with a bit more woomf (I would sometimes hit the limiter on the GS on overtakes). The twin cam GS just didn't feel a big enough step forward to justify the cost to change so, after trying the KTM SMT (great fun but a very sharp throttle action) I decided on the Multi.
The Multi has been great - I've now done 8000 miles, including tours to Italy and Germany. It's had some recall/upgrade work done by the dealer (Snells in Alton

) to improve fuelling and the power of the rear brake. It's been 100% reliable. Servicing is at 7500mile/10k km intervals. The engine is stunning and it is huge fun to ride. The luggage isn't as well-designed as that on the GS but other than that it ticks all the boxes. I find the Multi more comfortable than the GS - I used to get aching knees on the GS after a few hours but the Multi is more spacious.
So don't be put off the Multi by second hand tales of owners having problems - there are 9+ 1200 Multis in the club that I belong to and no one has regretted buying the Duc. At least 4 owners came from 1200GSs

and I think that you'll find that Ducati's quality is more than a match for current BMWs