Interesting proposal, although the wording of the 'contingency' legislation is weak and I don't see how it could be made adequately strong.
The problem is that I don't see any good way of writing the legislation to ensure that the states really act in 'consensus' fashion. Suppose, for example, that states comprising 490 electoral votes pass this election (leaving 48 votes cast by states that don't). A couple of the states that passed such legislation, comprising 5 electoral votes each, balk at splitting their electoral votes because it would throw the election to their non-preferred candidate. They each argue that since [the other state] hasn't accepted the 90% criterion as having been yet met, [the other state] is required to cast its EVs as winner-take-all. Thus, the 90% criterion hasn't been met and so the state must also cast its own vote as winner-take-all.
Things could get very bizarre.
So they write "contingent" legislation that kicks in at a certain time, provided a stated number of states have acted. The trigger date should be 1 January, [Election Year]. The law has to be in place then, since candidates shape their campaigns based on the parameters of election laws. So those laws would be in effect long before anyone knows how the Electoral College votes will shake out.
John / Billybob