Just as an anecdotal on brakes and the demands of tandems...
There have been two situations where having only rim brakes on our road tandem were we (me) were flirting with a potential brake fade / rim heating problem:
1. Any time we get caught behind cars or motorcycles while descending steep and twisty mountain roads, to include our local ~2mi / 8% ave. climb/descent at Kennesaw Mtn.
2. After cresting Tepesquite Canyon road whilst riding between Santa Rosa and Solvang, instead of being treated to an refreshing and exciting series of fast twisties where we could amortize the last 30 minutes of climbing in 120* heat, we discovered that part of the road had not yet been repaired following severe weather and was dotted with hundreds of washed out potholes.
In both instances, instead of being able to let the tandem "fly" between corners where max braking would be used to control speed through the corners, the unexpected / unwelcome impediments created a situation where we (me) were forced to alternatively be on the front or rear brake all of the time to control speed without the benefit of fast flowing air moving across the rims to aid in rim cooling.
It has been these rare and unexpected situations, along with the occasional descent in the rain, that has compelled us to use the front rim brake / rear disc configuration on the tandem(s) that we'll most likely be riding when we encounter these high-brake demand situations.
If you never venture into the mountains, it's not really an issue. But, for those who do it provides an alternative to the tried and true methods of dealing with the unexpected heavy demands that put high heat loads into the tires of a bicycle, e.g., stopping mid-descent to let things cool off, hauling around a 2 lb Arai drum brake that's rarely used as anything more than a parking brake, or being unware of how heat loads generated by the rim brakes and tire friction can combine to unseat a tire bead in dramatic fashion.
Just some food for thought and some insight into why Avid rear discs have been embraced by many teams who do encounter mountainous terrain on a semi-regular basis.