100% support to such kind of initiatives
The US Constitution isn't actually very clear on the process for parts of one state voting to join another, most likely it would fall under the category of two states merging (which requires the consent of both state legislatures as well as Congress) but this isn't 100% clear. Certainly this should show the way forward and the GOP should begin pushing for a Constitutional amendment to allow counties to join neighboring states as long as the county itself votes in favor of the move by referendum, the receiving state legislature votes to allow it, and the land area is contiguous and does not split the original state in two geographically (state the areas are leaving don't get a say). In addition to the Oregon counties that just voted to join Idaho, this could open the door for:
-Eastern Washington and far northern California to join Idaho
-Inland areas of California to join Arizona, Nevada, or "Greater Idaho"
-Most of central New York to Pennsylvania
-Much of southern/western Virginia to West Virginia or North Carolina
-I personally think Georgia going blue in the 2020 elections was an anomaly and will right itself, but if not much of the state could conceivably join Alabama, Florida, or South Carolina
-Downstate Illinois to Indiana, Missouri, or Iowa
-Much of Minnesota to the Dakotas or Iowa
-Much of Wisconsin to Iowa or Michigan
-Much of Colorado to Utah, Wyoming, Nebraska, or Kansas
If the Oregon counties can successfully pull this off, which IMO is unlikely but not impossible, it will be an absolute game changer in terms of reshaping the political map (which of course is why the left will fight tooth and nail against it).