There are only a couple of states that do not include intubation for RNs. However, it would be impossible to maintain the skills of RNs if they did intubate in the hospital. Even the smaller ICUs employ over 60 nurses. Larger hospitals can have almost 1000 RNs working just in critical care. As well, who would be fetching all the meds and setting up procedure trays. Believe it or not, doctors and PA students don't always have access to the drug machine and some have not found their way around the storeroom. In an emergency, there should be priorities and job descriptions to avoid confusion.
Our RNs share intubation with the RRTs on all of the transport teams as the RRTs also do some of the procedures that is usually included in their job set. Both must still get 10 intubations in 6 months in addition to the other advanced procedures. Each must also get 25 tubes in their initial training to intubate. Since RRTs are considered primary intubators in Neo, to apply for the transport team they must have no less than 100 intubations and 2 years of NICU experience which it takes 2 years of other RT experience before being accepted into NICU. So you can see how difficult it would be to have the same requirements of a group as large as nursing remain proficient at intubation.
For Flight, if hospital based, the RNs can get their procedures(intubation, central lines etc) in the ED or ICUs. Many also will still work the ICUs on their off days just to maintain proficiency with their RN knowledge and skills since Flight may not give them many patients and medicine changes quickly. They hate to arrive at a facility and pick up a patient who is on a couple of drips they had no idea was even available.
It would also not be feasible to have a Nephrologist have intubation privileges since it is doubtful he/she could meet the requirements to maintain competency. The best person for the procedure should be the one providing it. That also includes the education and what to do after the tube is in. Those who intubate at our hospitals also must know what tube the patient requires and must be thinking about tomorrow and not just one skill at the moment.
I'm sure your hospital has a book or section on their computer intranet that lists all the physicians and what each has been given invasive procedure privileges for. We take the competencies seriously and are allowed to tell a physician to step aside if they are not cleared by the various medical directors and chiefs of medicine or critical care to intubate.