An unexpected ray of hope

Cast a wider net. There are many schools out there. Take the lack of interest in the #1 school as a true indication of their interest. When a RC has real interest, you'll know it.  Until then, keep pressing. Also, he doesn't need to keep emailing every month, it's not a good look.

First, definitely do a wider net. The number one school doesn't sound very promising right now.

BUT

My 2018 also had a top school. They had invited him to a camp as a sophomore, he went, and got back the standard "if we want to recruit you, we'll call you" and they didn't. But during his senior season, my son (a RHP) texted the recruiting coach after every start with his stats, a highlight or two from the game, and usually a nice word for a teammate or two, as well as a note about when he would pitch next. About halfway through the season, the RC apparently came to a game. Then the PC came to a game. First we knew about it was when the HC showed up and sat behind home plate in all his Big College gear and son threw six and two thirds innings of no hit baseball.

They made him an offer in September and he committed. 

So don't give up hope or reaching out when there's something to tell them, but also note, son was sending that same text to about 10 different coaches and had several other options before the dream school came to the table.

I'm wondering why you are calling this a "ray of hope".  If he was a 2018, maybe, but as a 2019 the real action is just starting. There are no "rays of hope" right now, the world is his playground, until told otherwise

Since they've told him that they look forward to watching him play, have him update them with his 2018 playing schedule once he knows it. Until then, I'd let it lie.

In line with others' recommendations that he broaden his approach, he should do the same with those schools/programs that line up well with the characteristics of his #1 choice.