What are the practical limits to shelf life of beer? Could one brew any beer/ale with long shelf life in mind using different techniques? For example: brewing at higher levels of alcohol, does that change shelf life?
Shelf life is a pretty complex subject, and is usually best to talk about on a case by case basis. But basically speaking, the higher alcohol a beer is, the more gracefully it will age.
Barleywines, Old Ales, and Imperial beers can all be cellared similar to wines, and these beers tend to age very well. In fact, it would be a shame to drink many of these beers too young, as it takes a while for the flavors in a bigger beer to meld, and for it to mature.
Smaller beers tend to hit their peak flavor much more quickly, and then taste progressively less tasty as they age. There’s no reason you couldn’t age a small beer for a long time, it’ll just never taste as good as it did at it’s peak.
Hops have some antibacterial qualities that help to combat certain infections. Still, throwing a ton of hops into a beer won’t make it an infection fighting dynamo. Take Lambic style beer. Lambic has TONS of aged hops thrown into it, which are used to fight off certain bacteria (lactobacillus). Still, other bacteria (pediococcus) and wild yeast are main contributors to the flavor of these beers.
Also, hop flavors fade with time. So beers with dry hops or lots of late boil hops should be consumed rather young.