Same concern here because of the E3 series.
Did the E3 processor itself cause the lack of reg ECC support or 1155 motherboard restricted it?
I THINK it was the processor itself, as it was basically SB with a ECC support tacked on
SB-E was delayed partly because it was a massive new memory controller with support for a ton of different standards.
I also think E5-16xx supports reg ECC but need prove before emptying my pocket.
Well for now it's a moot point as it's not for sale anywhere
But for further circumstantial evidence, look at the dual socket 2011 server boards and they support registered memory
You could argue that maybe that's only for E5-2600 series, but I doubt it