If the rumours of a 12 team top league are true then IMO there will have to be a significant reduction in doubling up.
The second tier will have to become a hybrid Champ/NL strength which just would not be credible to combine 3/4 riders of the standard of this years Champs No7 and below and riders such as Cook Harris Masters King Holder etc
Id say no rider over 7 by this years Champ figures should be allowed in a 2nd tier like that.