This thread started with the PO saying (s)he was "Not sure if my son is a D1 possibility or not." Where the thread went was a discussion about D1 vs. D3 recruiting. The timelines and much else about them are pretty different, and that's why advice about one is not necessarily relevant for the advice about the other (or JUCO or anything else). A player in this situation has to understand both, that's where it gets complicated.
The most frustrating statement to hear is "could be D1 if his numbers get to D1 numbers." Neither you nor anyone else can really tell whether that will happen or not. Really, there's no such thing as "possibly D1." At any given moment, for recruiting, there is either "D1" or "not D1." If your numbers (fastball, 60-time, pop-time, exit velocity) are D1-level numbers, then you should be getting exposure right now, whether at camps, showcases, games, etc. If not, then getting seen by D1 coaches is not going to accomplish much.
What "don't showcase until you have something to show" means is, if you are a pitcher and you are not at 90+ (88+?), then D1s will not be interested yet. Especially if you are shorter than 6'. Sure, they might keep an eye on you (and dozens of others), but they won't do anything until you are actually what they want - so, why pay the money for camps before they would actually care? Coaches are less interested in kids with potential than they are interested in kids who are already there - and there are plenty of those. If/when you hit 90 (88?) that is the time to go to camps, showcases, etc. - or just be seen in travel games. If it's the summer after junior year and you haven't hit that number, that's when all levels from D1 to D3 will be recruiting, so then you go to camps, etc. of schools that are a good fit.