A feature of GE's CF blades is that they're reportedly quite thick at the root. They have to be like this so that they can stand the radial forces trying to pull the blade apart.
This thickness hinders airflow into the core; it is aerodynamically unsatisfactory. In effect GE have to strike a balance between aerodynamic freedom (they can make the blade any shape they want) and structural requirements (there is a limit to what can be achieved with the CF technology they use).
RR's point of view with hollow Ti blades is that they can be thin at the root. This improves core air flow, and (if the
PR blurb is to be believed) the improved core efficiency makes up for any losses caused by additional weight, or the fan blades not being the ideal aerodyanic shape. Clever though they are, there are almost certainly some limitations on just how curvy RR can make a hollow Ti blade (though looking at various examples shows that they're pretty good!).
And, casting an eye round the Internet, I think we have to conclude that both GE and RR's engine performances are remarkably similar considering the quite significant differences in architecture, materials, etc.
The thing that GE might be worried about is that RR now seem intent on doing a CF blade that is thin at the root. Not only might this be lighter than GE's blade, but it would have better aerodynamic performance especially with regard to core air flow. They've been flying these in the Advance demonstrator engines. And they've apparently done a lot of work in automated layup processes, saves a lot of manpower in manufacturing.
If RR can make those blades work, we might see some interesting upgrade options; want a CF fan blade set on one's old Trent 900s? Could almost be a ramp upgrade...