I wish him the best of luck, and hope I could do the same. I could only imagine how quickly I'd improve if I had the time and money. I can see him getting to +2 at least, although I do feel like he should be further along than he is, that's for sure simply based off of the amount I've played.
Calculating that I've played every single weekend, 5 hour rounds, plus approximately 3-4 hours of practice or 9 holes throughout the week, for approximately 7 months each year (stupid Canada) in the past 4 years, that would put me at about 1,680 hours which is on the generous side for sure since the calculations were general and I haven't strictly played that much. Myself being a 2.5 handicap, and only 17% of the way through the Dan Plan of 10,000 hours, he should definitely be doing better even though he's chosen to learn the game in a different way. I still think that he has a huge advantage just because of the amount of time he has devoted to it.
Will be interesting to see what happens.