I think a £100 mark up is unlikely. Maybe £50 but not £100, google's objective with the Nexus 7 was always to keep the price low and I don't think a bump in storage capacity will change this, especially given the impending iPad mini and the inevitably huge sales it will generate and the huge proportion of the sub 9 inch tablet market it will take.
To be honest, we all know Google has no plan on giving the nexus line removable storage. But at least they are acknowledging the fact that people still have a need for offline storage. I am glad I waited as the Nexus 7 has now gone from a device I was on the fence about due to the low storage capacity, to a device that is worth serious consideration.