There is no big change regarding LM P3, it is essentially a replacement for LM PC. The only significant difference is that instead of the Oreca FLM controlled package, it will be 'open chassis, single engine', opening the door to emerging chassis manufacturers. Like FLM/LMPC the P3 class will also not be invited to the 24 hours of Le Mans.
My interpretation of that news release does not include running LMP3 at Le Mans. Sounds like the evolution of American Le Mans Series (deceased) LMP C which can still got the short end of the stick for United Sports car merger.
LMP C are all Oreca chassis with Restricted Corvette V8.
Phil