This is a great fare for what's available now. However, the Discount carriers like Jet Blue don't have their schedule open for then yet.
The other thing you might want to consider is that Delta (and all the other major airlines) might change their flight schedules 100 times between now and next October. Since you are flying in from overseas, you won't be as flexible with what changes you can live with, since you need time to go though Customs and Immigration, claim luggage, and take the Airtrain to the other Terminal and go though Security again.
What I would recommend is that you book your flight to Orlando through the airline you are using to fly from Australia. Most of the airlines are partnered with others in a Global network. That way, they are responsible if your first flight is delayed or changed. They would have to rebook your connection and you won't be responsible.