Use the data that is there, such as “only compatible” up to 2.5, with the understanding that maybe it’s not always 100% accurate for your usage requirements. Or, at least have to option to use the compatibility feedback field for searches. A plugin already lists info such as 31 people say it works with WP 3.1 and 3 people say it doesn’t, to display the little boxes like “Works!” or “Not Enough Data”. Sure, it’s not a guarantee, but data is there that could help narrow down searches.
