I think this is the biggest thing saying "they're not coming", lol.
There's no group for DP/LMP2 cars, and there was only ever space left for the Gr.2 cars.
Having LMP2s compete with LMP1s would be daft - because it's not just about whether they could be BoP'd to match - it's about what they are and how they're seen, and while LMP1s and Group C represent the coolest, fastest cars: LMP2s are just "some close-to-spec race that happens to be on the same track as those cool LMP1 cars".
Even Forza doesn't make this mistake.
(And no, the new DPis don't count as "the coolest, fastest cars" either.)
I doubt there's ever been any plans for more groups since Gr.2 (I mean, what would a P2 class be called anyway?).
It would be nice to get a full rework of all the Groups (N100 split for there to be an N50, optional "no Vision car" - basically LMP1, Gr.C, GT3, GT4 - groups for Gr.1, Gr.3, Gr.4, an actual FF Gr.4 group, electric groups, two Gr.X VGT groups, '60s Le Mans group, P1 GTR / Zonda R group, all the other suggestions people have made).
But the game is creeping closer to end-of-life. If any of this was coming, it would've appeared earlier on, or we'd have heard from PD about it. Changes to groups would affect the FIA series (whereas new tracks are kinda just a thing that happens), so I feel they'd have to announce those changes before making them.
Anyway. Laguna Seca. Yay.