For some number of pixels, it is going to reduce (halve?) the amount of light that is received by the photo diode.
If this is the green pixels, as suggested by some diagrams, then it may make little/no overall difference as there are already twice as many green receptors as there are red/blue.
Additionally, this means that there will be some pixels that do not record the same level of light as others. This will need a bit of new fancy footwork for raw converters to properly evaluate what it means to have a pixel that is not and will never have the same luminosity as all of the others around it.
This has potential to have an adverse impact on noise simply due to there being less signal available.
Will be interesting to see the outcome!