I have questions, with the qualifier that: Yes, I know there are always rare exceptions.
Why would you want to walk on at a D1? Just to brag that you "played" D1? Don't you want to go where they want you? Where you know you have a reasonable chance to actually play? Is this a matter of Baseball being a low priority for you, and you want to go to a school mostly for the academics? Then why would you go through the immense amount of work it takes to be on a D1 team if you aren't going to play?
I guess it could be pretty cool to be on the bench of an SEC team or a major D1 team that goes to the College World Series etc, but the chances of a walk on even being on the travel squad is really remote.
I could see someone who is a Baseball lifer who knows he won't go very far as a player, who wants to be a coach, going to a specific D1 to learn from the coaching staff.
But a player wants to play. I really think it'd be a far more rewarding experience being in the starting lineup at a D3 than sitting the bench and never getting an at bat at a D1.
If you are a "late bloomer", why not go to a JUCO first and work on developing for another year or two?
As I said, I've got questions....