Sorry for being so late replying! Yes, I pretty much think that WiPs starting in old canon timeline are fair game always, and, to a lesser degree, pre-existing plotbunnies probably as well. If I were heretic I'd say if Harry can shag Draco in a plot, he can just as well do so while Sirius is alive ;). But of course you're dead right - working with current canon is a far greater challenge.