I don't see a good one. It doesn't seem to help voters like me participate in the system. A cynical person might see this as an attempt to work alongside the court battle that is currently ongoing to maintain the disenfranchised status of expat Canadians.
The legislation says it's in response to Justice Penny's decision to account for the new numbers of recently enfranchised voters. I don't know what was broken about the system before, or what in the system before was incapable of accommodating these same voters. Again, as I said in my opening statement, this seems to be a solution in search of a problem, or it seems to be a solution for the problem of newly enfranchised expat voters.
To your earlier statement about drivers' licences, when I moved to Maine after grad school for my first position, I got a Maine driver's licence. Until that time, for seven years, I had held onto my Ontario driver's licence, mostly because I was a poor graduate student who couldn't afford a car. I finally was able to buy one, I registered my car, and I needed a Maine licence.
I asked to keep my Ontario driver's licence as a souvenir. My mindset was that it was my hope to return to Canada as soon as possible, as soon as I could find gainful employment there. But the DMV in Maine said I must relinquish my licence, as they don't allow two licences to be kept. The same was true for my wife when she moved to New York state. The same is true in New Jersey, where I currently reside. This is a common practice.
It is my understanding—and again, I would want to double-check my figures—that the majority of expats live in the United States. They are all facing a similar situation, if they choose to drive.