The fix... my ideas haven't changed on this for some time...
First, make WEC a LMP1 championship only.
WEC races with ELMS and ALMS at select events. Say two ALMS, two ELMS, plus LM. Participation in WEC requires full participation in one of the ALMS or ELMS. If AsLMS ever actually gets off the ground (
) then we can incorporate them as well.
GTE-PRO ends up with 8 entries, GTE-AM has 10 entries, if you assume that the two "American" entries go away, but the remaining stay. Even if you only include 18ish GTE entries, and a dozen LMP2 entries, ELMS now has a good field, as you've taken away the option for GTE cars. ELMS is strong again.
With restricting WEC to LMP1, you also are highly unlikely to end up with entry numbers issues, so there will be no issues with running at Petit Le Mans, Sebring, Silverstone or Spa. ELMS is back to running at the classic tracks, with no other real competition for LMP2 or GTE cars.
It is probable that both the ALMS and ELMS will pick up top level LMP1 teams that they don't currently have. It might also be probable that Dyson or Cytosport would consider running in the WEC, as it only adds TWO more races to their schedule.
The "National/Domestic" series need the entrants and the quality, and the LMP1 manufacturers need the status of the WEC.