I am baffled by a lot of these timelines. Surely Nokia has got the next set of devices already in the testing phase. I mean we are talking MS and Nokia announced the purchase a few months ago. I see no way there aren't a wave of Nokia's waiting to be given the green light and set on their way. Does anyone think a company like Nokia would rest on the nearly 6 month old 1020, even older set of mid-range devices, and only continue to market the new L525, 1520, and the as yet unreleased L929 as Android's pump out their next wave of phones? What if the sale had gotten side tracked? What if it just took 4-6 months longer then expected?
What if China STILL holds it up, just because they can?
Nokia will have something out in that time frame.
But, on back to the query at hand, I think you should give the L929 a chance to come out, and grab the phone you like best between that and the Z30. If you choose the Lumia 292, do not worry about WP 8.1 phones- the L929 will have a more then strong enough processor, RAM, and graphics processor to handle the entire update. The High Def screen will still stand up to any other screen tech coming out, and you will be out nothing.
I like BB10, so I understand the appeal of the Z30. If you believe BlackBerry will be in a position to support it, then I say go with your gut after seeing them both in action.
Don't wait unless you really have a gut instinct to.