The FAA has finally
published the AD. Basically, you need to either disable it or give it an external GPS source (the later option is probably the cheapest for those already invested). If Navworx modifies the firmware to report SIL 0 again, then it would also fulfill the terms of the AD but would not meet the 2020 mandate. And, on page 8, they specifically call out that this does apply to experimental aircraft.
It comes down to the use of a non-TSO GPS source (an off-the-shelf SiRF IV, which going through a couple owners, is
now owned by Qualcomm) and claiming a non-zero SIL.
Attempt #2 at this whole Sonex Business.
Waiex-B WXB0019 [Progress reported upon completion]