Great question, our local 1/8 track in Miami doesn't require it (see link here: http://www.countylinedragwayinc.com/rules.htm) plus the purpose of my build is to have both a street/strip car so I can enjoy, daily drive my ride dude.
Most likely in the near future I will upgrade to a full rollcage, aluminum seat with 3" inch SFI rated harness, that will be estimated after I re-tune the car.