Phoenix-Tucson I-10 Super Corridor
Could continued strong population influx into Arizona cause Phoenix and Tucson to merge into a common mega-region one day? This article suggests that current trends make this a possibility. The core areas of Phoenix and Tucson are separated by 120 miles. As a point of comparison, Dallas and Fort Worth are about 30 miles apart.
https://www.orionprop.com/topfive/could-population-growth-propel-phoenix-and-tucson-to-merge/
I think this is an interesting concept. Living in San Diego currently and seeing the population outflow from California due to severely off-balance Home Affordability indices and a growing reputation as an state unfriendly to business growth, I don't think that the current trends are going to be slowing down any time soon. It looks like there are several high-speed rail projects currently under planning in this region in Arizona which would also increase the feasibility.
Could other areas with massive recent population influx like Denver-Colorado Springs explore a similar possibility?