Thats exactly what I did, I traded in my 2007 oasis for the TI at the Hobie dealer, they gave me a great price for the Oasis (Used Hobies are rare, difficult to find and really hold their value well, I'm sure the dealer sold it within a week).
To add a jib you can follow my posting on adding sails ( I have 265 sq ft of sail area) ( viewtopic.php?f=69&t=33720
) titled ultimate tandem island (hydrofoils, spinnaker,jib,etc). It shows all the designs and could be applied to either an AI or a TI. I'm out every single weekend with my TI and just love it, it's by far the most versitile boat out there today, we even scuba dive off of ours (me and my wife, with 4 tanks, and all diving gear)