Does anybody really care about Jeb's endorsement?
Rubio does, and Florida's Republican Establishment does.
I thought Jeb! was about to endorse Rubio during his speech announcing the suspension of his campaign. He sort of did so if you read between the lines, but he did not explicitly support Rubio. I think Jeb! feels very betrayed by Rubio. He shouldn't, in that Rubio was being recruited to run for President before Jeb! and his entourage felt it was safe for a 3rd Bush to give the Brass Ring a shot, but Rubio attacked him hard (although Jeb! attacked Rubio harder).
If Jeb! really wants to be President, he ought to (A) endorse Rubio now, and (B) run for Florida's open US Senate seat which Rubio is vacating. There's always 2020 and 2024, and the Senate seat from Florida could give Jeb! an opportunity to sharpen his conservative bona fides. If Jeb! wants the Presidency to be handed to him, that's not going to happen, and such a desire would say a lot about Jeb!, none of it good.
I really doubt Jeb! runs again. I actually hope he goes back to the private sector. He'd be happier there.
He'd also be one of the few Bushes with a real job. I was looking through their family the other day. Not many who don't work as lobbyists or in elected office.