[stoppingdown]

Not really a paradox if you consider a buy timeline. The Tamron 150-600mm is an interesting possibility, but it's not in my immediate list of buy - also because at the moment it would require an e-mount to a-mount adapter and I think there are chances that from here in one year a similar lens with a native e-mount might appear (Sigma, for instance, recently commented about the possibility of "porting" more lenses to e-mount). Furthermore, for wildlife I'd give precedence to a lighter lens around 300mm, which at the moment doesn't exist for the e-mount. Perhaps such a lens + 1.7x would make the 150-600mm useless. For purely glass lenses, so, there's nothing I'd buy in this year, waiting and see how the market evolves.

 

Instead, an 800mm mirror would be cheaper (at least I suppose), with far less expectations that a glass lens (in fact I'm just thinking of it for very specific usages) and I could buy it in the short time.

 

Summing up, I see:

1. something around 300mm ƒ/4, or perhaps a zoom in that range ƒ/4.5-5.6, e-mount, for wildlife and BIF, hand-holdable - it doesn't exist and I think it won't in 2015
   
2. a longer zoom lens, such as the Tamron 150-600mm, for more reach, not handholdable, usable for the car or a hide - it exists, but not in native e-mount. I wouldn't buy it, anyway, until there are some hints about how the market for #1 come out, since both #1 and #2 would be a relevant expense.
   
3. a 800mm or such mirror lens, with any mount (because I imagine there's and will be nothing in native e-mount) that could be useful very specific cases, cheaper
   

#3 is the only immediate chance I see.