As appealing as it is, I don't think I would use a barrel, just for sake of practicality at my house. Your point about introducing contaminants over repeated pulls is a good one. Although a RIS should have a good amount of alcohol to mitigate that risk, over years of pulling and replacing, you're right, I could see something taking hold.
I considered either glass, which my sour solera will be, or stainless steel (i.e. a corny keg). I think your point warrants that a keg would be better than glass. I can go into and out of a keg without ever opening it.