It's December of his senior year? I would assume he's starting to hear back from schools.
Was he not accepted by his first choice(s) and hoping baseball might be able to help increase those odds? Does he need another year of grades and a few more cracks at SAT/ACT?
Ivy is quite a bit above NESCAC/Centennial baseball. If you think your son will be good enough to be recruited by an Ivy in a year, he'll probably be good enough to walk on at a D3 next Sept.
Has he been in contact with any D3 coaches? D1?
If he were a fringe D1 prospect that didn't find a landing spot - I might consider it. If things were cold prior to signing day I would be focusing on the best possible academic situation and let baseball figure itself out.