The way I see it, Sports Cars Racing is much more about particular races with their very own distinct identity then about series or championships.
Sure, regional championships (north america, europe, asia) are needed to keep the teams running and the drivers busy, but - unlike what happens in F1 - a sports cars racer and a sports cars manufacturer will be remembered for wins at races, not championships.
Take, as an example, Johnny O'Connel. Here is what is written on his twitter account about him:
So, I think it is wrong to keep LMP1 cars out of whatever series results from this merger. Not that LMP1 teams will care much for full entries. But they will care about:
Sebring
Le Mans
Spa
Daytona
Petit Le Mans
And Rebellion's "visit" to Petit Le Mans last year is significant, there you have an european based team making a monumental effort to be present at a race that didn't give them anything relevant for any championship, why was that?
Exactly ... they got a prestigious win in the sports cars world. Something to brag about. And be listened. Not to mention respected.
I know this post is confusing, but I hope I'm understood. It's all about individual races, and it would/will be a shame if the likes of AUDI, TOYOTA, ALPINE-RENAULT, PORSCHE, NISSAN can't dice it out with their big LMP1 cars in prestigious north american races, apart from the one and only WEC event to be run there each year.