The new 650S racer was designed to meet the GT3 regulations used in second-tier sportscar racing series around the world, like the Blancpain Endurance Series and the Pirelli World Challenge. Top-tier series like the FIA World Endurance Championship and United SportsCar Championship, however, use their own GTE regulations (adapted from the previous GT2 regulations). Discussions over converging the two sets of rules (like DTM and Super GT have since) had commenced when McLaren GT was developing the previous 12C GT3, but those discussions ultimately fell apart, keeping the two categories separate... and in separate series.
Autosport reports, however, that in redesigning the 650S GT3, McLaren's GT racing division kept that disparity in mind so that the GT3 could be set up as well in GTE spec, enabling it to compete at the 24 Hours of Le Mans and associated series like the WEC, United SportsCar Championship, European Le Mans Series and Asian Le Mans Series.
We're waiting on word from McLaren as to the verasity of the report, but even if a 650S GTE would stand little chance of overtaking the faster LMPs like the F1 GTR did nearly 20 years ago, it would still be interesting to see McLaren (whether as a works entry or through customer teams) competing at Le Mans again.