The organization “Building a Better Colorado” has been holding meetings around the state to explore election reform ideas. This story describes the conclusions reached by the South Platte Summit. Notably, when the top-two idea was discussed, only 18% of the participants supported it.
That particular region is the most conservative and Republican-dominated part of the State. They likely see no reason for independents and Democrats to exist, let alone vote. It appears that it was not recognized that an immediately adjacent state uses Top 2 for election of its legislature, and has done so for 80 years.
Other areas of the State have been more favorable to Top 2, though one suggested Top 3. The question was framed as how to let independent voters participate in primaries. Colorado has closed primaries, and because of by-mail elections, it is difficult to use the ability to affiliate immediately before the primary.
The more favored solution appears to be a modified pick-a-party primary, where independents only would be given a ballot, with all parties listed, and they would choose on the ballot which party to vote for. Democrats and Republicans would continue to be given a single party ballot. Since ballots from independents would be recognizable, I suspect political parties would sue to have them excluded from being used.
Top 2 eliminates the need for partisan registration except for presidential primaries, but that is not a problem since Colorado doesn’t have a presidential primary.