This is not entirely true. Federal preemption is its own area of law, and any powers not explicitly given to the feds are reserved for the states. The ruling out of WY, although decided in a federal district court, was only there because it was a civil claim with complete diversity of jurisdiction (WY and MO) and the suit was in an amount over $75,000, which is the threshold for a federal case. The criminal case remained entirely with the state.
Even if upheld on appeal, the WY case will only apply in the 10th circuit, and with parameters as narrowly tailored as the one outlined by the judge in that case. Other states (like MT) will still need to litigate it, write cc into law, run a ballot initiative, or come up with their own solutions. Eminent domain is probably the least likely way to claim a public easement at a corner. The WY case gives a fantastic roadmap as it is to establish the public necessity of access at a corner, and I suggest reading it.
And if you are interested in a legal deep dive into where MT, as a state outside of 10th circuit jurisdiction, stands currently, then I suggest reading this, which also includes a link to the WY decision and pertinent case law:
https://www.backcountryhunters.org/thinking_about_corner_crossing_in_montana_read_this_first