Are tandem riders now shunned by solo riders, in the same way that motorcyclists don't acknowledge scooter riders (or Harley riders, unless you are on one)?
Yes and no. I think there are many interacting phenomena. In a random order:
1) It's never easy to ride a tandem within a group of solos, even if the solos are your friends. Tandems have a different acceleration/deceleration pattern, you go slower up hills, faster down hills, so in a long ride, tandems never stay in a group of solos for very long.
2) Some male riders (not all of them obviously!) are really put off by the sight of a man and a woman riding the same bike. I can't tell the reason for sure, but there's something on the line of "if a woman is involved, then it's not serious cycling". I would be happy to read the opinion of same sex tandems on this point.
3) We are not in a particularly good shape at the moment, but we live in a region where most cyclists are much older than we are, so we are still faster than a majority of them. Again, the same male riders as above sometimes (not always) react as if they were insulted when they are overtaken by a bicycle with a woman on one of the seats.
4) I don't know what your tandem is made of, ours is made of steel. Most solo riders have a fiber reinforced plastic bicycle. Some salesperson told them that fiber reinforced plastic bikes are light, therefore fast, while steel bikes are heavy, therefore slow. If you have a steel bike, you know this is not true, but it can partially explain our impression of being shunned.
Having said that, I should add, for the sake of honesty, that in most of our rides, none of these negative encounter happens. Enjoy your rides, and forget the rest!
A