Consider the already immigrated medical professionals living in the United States right now that are unable to practice because of the above described licensing issues.

To give a couple examples. If a nurse moves to the US and learns he can't practice without going back to medical school, he may opt instead to work a different job and defer his medical career. If a doctor moves to the US and is in the same position, she may choose to remain a stay-at-home mom and let her husband be the primary breadwinner.

There's also the arbitrage aspect here: globally we may have a healthcare worker shortage, but it may be more severe in one place than another. Reducing the friction involved in moving the workforce could allow workers that are in relative over-supply to move to an area with relative under-supply, improving the overall efficiency of the system.