I notice that the latest rev I versions of xmeg32D3 parts have dropped the remapping bug, so presumably this now works for this rev of silicon.
I'm a bit confused as to how the SPI remapping actually works. The REMAP register will allow USARTC0 to be nybble swapped, and in SPI mode this would normally put SCK on PORTC.5. However, there is also a SPI SCK and MOSI swap feature. So if I lay a board out with SCK on PORTC.7 as for a normal SPI peripheral, can I also use USARTC0 in SPI mode on those pins? It comes down to whether the swapping of SCK and MOSI is done in the SPI peripheral, or whether it also applies to USARTC0 in SPI mode. The documentation is ambiguous about this.