I have released a beta test of the TIE Interceptor as a msh/odf package rather than as part a map, so you will be able to mod it's performance right from the start. I have no plans to release it in .xsi format, but there are ways of getting it from msh into XSI...
I think it's unlikely I will make a TIE Defender, I never really liked the look of them that much. I don't know what it is about the TD, but they never seemed to me to fit the Imperial design ethos, and it's hard work to model something I have little enthusiasm for. The TIE Crawler is a more likely option, but not for a while.