Rojo, I think you're being too optimistic here. Fisher is an excellent runner, and won that race as easily as Cheserek won NCAAs (and in the same manner), but I don't think he's going sub-4 for several reasons.
Firstly, he doesn't like running for time--he likes racing. If he goes to the Dream Mile I don't doubt that he'll win, but he'll win with a fast last 200, or maybe a good last 600--he's not going to go balls to the wall and risk losing. Sub-4 is dependent on how fast Maton, Tamagno, and whoever else steps up can run in the mile. I'm sure Maton just had a crappy day, but who knows whether he's really going to be much faster than 4:03 in the spring, and who knows if Tamagno will even reach 4:03. Fisher would be just as happy to win in a comfortable 4:01 than to win in a painful 3:58--and much happier than if he lost with a 3:59 or 4:00.
Secondly, there's the unknowable factor. Injury, burnout, never had good weather, never had the right mindset or competition. I'm sure he likes running now, but what if he decided he didn't really feel like training hard and trying to go for sub-4? What if his newfound fame gets to him and he underperforms or hates running?
Thirdly, sub-4 is FAST! Verzbicas won by about 20 seconds when he jogged to a 14:59 his senior year, and then ran 8:29 for the 2 mile, and basically won everything in sight, and he still only ran 3:59.71 or something at the Dream Mile, with a high school pacer and Jantzen Oshier taking the lead all the time. It's just not an easy thing to do.
That said, if Fisher really wants to do it, and lucks out with training, weather, and competition, I could see him running 3:57 or 3:58. Certainly, he has it in him to break 4 in high school only competition, assuming that competition is fantastic and he pushes from at least 600 out. All the best for him.
No one in their right minds should bet against him again for the rest of his high school career.