Revoluntionary & friends:
In some parts of Oz that is indeed the concept - bringing the hospital to the patient. Sadly, it is fatally flawed; the only reliable research (ie that NOT presented by the medical fraternity with an agenda) has shown that the ONLY things that make a difference to outcomes (mortality and morbidity) particularly in severe trauma, are appropriate basic care and rapid delivery to an appropriate facility. Neither of these needs a doctor; in fact some research shows that systems that have doctors on board spend far more time on scene than those without, for no better outcomes.
In the case of intensive care transfers and retrievals, a doctor is often and wisely a part of the team, likewise for known specific incidents (like an entrapment requiring amputation) but for 99.8% of out-of-hospital stuff, in near 20 years in the game I've become a firm believer that out-of-hospital emergency medicine is best managed by suitably trained and experienced paramedics.
As far as aircraft go, all the EMS birds in this State are twin IFR, as a result of losing 4 aircraft and 8 lives over 10 years, all in single-engine VFR helicopters. One (wannabe) operator is trying to get into the game in the far north, with a single Squirrel, but as all emergency services and health personnel are banned from flying in it, they are not likely to get very far.