Sure, if it stays closed to the rule 40 nominees after the first ballot.
But what if the GOPe is telling Cruz that he'll win the second ballot to keep him in the race now to block Trump from getting an outright majority, but then they revoke rule 40 at the convention and open round 2 to any nominee? Or, more likely lower rule 40 to 4 states and then get the New England states to give their delegates to Romney so he can meet the threshold of delegate support to be entered into nomination in round 2?
Remember, rule 40 doesn't say the nominee has to WIN a majority in 8 states, they just have to have the SUPPORT of a majority, however that support is obtained. That will be how a non-contestant will enter the convention, and Cruz will be left abandoned at the altar.
-PJ
The Convention Rules are adopted by the convention delegates as their first order of business.
Last time around, Romney was able to cram through changes to Rule 40 (increasing the eligibility requirement to 8 states) because he controlled a majority of the delegates. This time around (assuming that neither Trump nor Cruz locks in the nomination before the convention), any changes to Rule 40 will have to be voted in either by (a) both Trump’s and Cruz’s delegates or (b) either Trump’s delegates or Cruz’s delegates joining with the delegates pledged to the other candidates.
I just cannot see any reason it would be in the interests of either Trump’s delegates or Cruz’s delegates to expand the list of eligible nominees.