It looks like he was saying XF more to get the right ballpark picture in the readers' minds rather than the exact car. Neither the shell nor the chassis that the XFG uses make sense for a large V8 MR layout.

And whatever we get, it should be something else than yet another inline 4.....

Quote from Breizh :

He didn't say it had to have the XFG/R bodywork.

MR can use XFG body, V8 must use XFR body