The Remington 700 as we know it will not handle the head size of the Lapua case, just as it will not handle the head size of the .378-.460 Weatherby...
Remington is not going to alter their extractor system, so they would have to make a larger diameter bolt and action for the Lapua.....
Many alterations have been done to 700 actions to handle just about every cartridge out there, but not as a factory project.
I still think the rumour is an old one from before Remington came out with the Ultra-Mags...