Has anyone been through any of the Gateway programs? If so, how is the success rate of going from a piston twin directly into the JetBlue world?

I believe it’s a 100% success rate.

Success rate is at or near 100%. I don't know where you are in your flying career, but for the gateway nowadays, I would actually recommend ExpressJet. Turbine experience, better flight benefits, commutable, and you can also opt in for a pathway to United. The ExpressJet to JetBlue path takes a little longer than the Cape Air path, but it gives you more options.

The ExpressJet to JetBlue program is only for pilots who graduated with an Advanced Aviation degree from an approved school. And with saying that, believe the program is on pause for new guys applying with the Delta contract going away.

True about the eligible universities... however, the wind-down of the Delta flying doesn't affect the JetBlue pathway.

Given the current state of XJT, this may no longer be true.

To my knowledge, no new Advanced Gateway candidates are being considered at XJT for the time being.

I'm not aware of that. To clarify, I was speaking in reference to the University Gateway program, which may/may not apply to the OP.

As far as XJT, it's a transitional time and a tough situation for those on the ASA side - many of them are understandably leaving. The overall outlook for XJT, however, is better than it was a year ago.

I thought that ExpressJet was losing flying left and right as well as aircraft? I heard its like the Titanic only on fire as well?

I mean no offense, but I think I smell a recruiter. Do NOT go to XJT. I had many, many, many happy years there (mostly in the right seat) and honestly enjoyed it despite its being mismanaged into the ground after the SkyWest buyout. But there is no contract on the horizon, no new flying, no guaranteed pathway to anywhere, and industry-trailing compensation there. It’s a shadow of its former self.