http://www.lemans.org/wpphpFichiers/1/1 ... n_2014.pdf
page 6 : Note that a private entry can race with Hybrid LMP but a manufacturer can't race with non-Hybrid LMP...
From page 9 to page 15, you'll see that the aero isn't going to change that much.
page 14 : in fact, to adjust the front element during pitstop is easier than changing the whole front cover.
I saw two main reasons for the success of group C at the time.
a) a fine regulation.
b) a lot of competitive private entries (most of them with the affordable Porsche 956)
For (a) the 2014 reg onwards may be allright.
For (b) I doubt that a big manufacturer will put on the market a Porsche 956-like 2014 Hybrid-LMP.