I'm not sure what's more impressive for nature to pull off, advancing a west coast spot up half a zone or an east coast spot.
I welcome the warming, but here, in the East, the continental influence is so strong a factor that a region could warm up a full zone, then, every 5 years or so, a "reset winter" will come along and wipe out any marginals that were beginning to take hold. And the injustice of it all is it only takes one or two nights of an Arctic blast to accomplish a reset even if the rest of the winter was "mild."
The net effect is, over my lifetime, I've seen the following plants go from truly marginal to almost bulletproof: camellias, southern mags, crape myrtles. Now, how much of this is due to milder temperatures and how much is due to hardier cultivars coming on the market of all 3 species? My guess is that it's a bit of both.
The way the winters since 2012 have played out (cold) ensure that we won't be seeing any palms spontaneously germinate in the general landscape anytime soon. In fact, I think those winters have kind of brought an end to the hardy palm fad that nurseries and box stores were plugging the last decade around these parts.