Currently only three upgrade items for the ETHA (meaning, you can buy these today):
1. Barrel system (pick one, as long as it's Autococker threaded)
2. Trigger (currently only Violent is making aftermarket triggers for the ETHA in 2 styles)
3. Planet Eclipse POPS ASA 2012 - while it's not necessary, you can swap out the stock ASA for this one
We're all still waiting on the EMC kit, which I heard today will be pushed back to mid-July for its release.