TBH I though they where going to do something with Devoted of Sigmar when silver tower was release and they designed the Excelsior Warpriest, but it ended up that only the Darkoath Cheftain was the only hero that got a future release in the end.
with regards of legacy army, I think GW is model and hobbyist company first and competitive wargaming seconds, that why they keep selling those models online without transparency if they get an update in the future.