150 flights to where? I get that they want to make good on their commitment to Boston, but Boston's not that big of a market.
They are going to have to increase flights to Chicago for starters.
If Virgin America goes away they can increase LA and SF flights too.
Domestically, they would need to start Houston Hobby, Savannah, Louisville and maybe an extra Midwest destination. They had their chance to jump into Kansas City and St. Louis and gave it up to Southwest. They may have to tango with Delta in Atlanta/Detroit/Minneapolis at some point as well
"Semi-internationally" they may want to try a secondary Puerto Rico airport such as Aguadilla
Internationally, I do not think they can do much more that would add daily flights with the exception for maybe Port-a-Prince, Haiti. 1-2 Weekly services are possible for Antigua, St Lucia, Barbados, Puerto Plata.
I think 150 flights would be during peak summer travel season and you would see a low during September-October for heavy maintenance.
JetBlue wants to make Boston a hub to feed their international partner airlines. That's why they are building the security side people mover/walkway from terminal C (Jetblue's exclusive terminal as of 2014) to Terminal E, international terminal. Boston is closer to Europe, the Middle East, and and India than any other big US city and could be a huge hub if the politicians, neighbors, infrastructure and runways could handle it. Even with things the way they are, it could be a larger international hub than it is.
They should be praying for Turkish, Emirates, or Qatar to get to Logan by then.
I wonder how many connections they are getting on the Japan Airlines flight right now?