So, a thought struck me as I was drifting off to sleep last night.
While the current material of choice for wooden casks is white oak, this certainly wasn't always the case. (I know that 'traditional' balsamic vinegar, for instance, is aged in as many as three different woods.) I would imagine that liquid-tight casks could be made from nearly any good, close-grained hardwood (fruitwoods, mostly). What sort of wood character would have been imparted to the brew by these?
Nowadays, we homebrewers have started playing a bit with oaked beers, adding oak chips to our fermenters & letting them soak in the brew for a while...
And this is when the light bulb went off: I've got a bag of apple-wood chips (nominally for smoking things) that I could use in the place of oak chips. I almost certainly wouldn't get the depth of character that I'd get with oak; I imagine it would be significantly more subtle, and I'd have to be careful what brew exactly I used it with, to not overpower the wood. But it would be interesting. And I can easily get similar bags of chips of different woods--cherry, maple, etc.
I've simply gotta try this. Something for me to play with over the winter brewing season, I should think. I imagine a nice Vienna lager, with maybe either apple and/or maple. If preliminary tests go well, perhaps a brown ale (or even a porter?) with some cherry.