This is essentially what you have with TABS. A simpler GPS for ADS-B approval able to be based on COTS GPS but not to meet the 2020 Mandate. This is all an old discussion that has been gone over here before. You are wasting effort trying to reinvent the wheel. Time would likely be better spend understanding more what today’s technical options really are and working to improve those and regulations around them.

You can’t just have any old COTS GPS connected up to some ADS-B Out systems and have others see them without lots of potential issues. For the system to work both IFR aircraft and ATC needs to “see” VFR aircraft and trust their ADS-B Out GPS is working and accurate (both for not false positive threats or negative notice of real threats). The current situation where the ADS-B ground infrastructure and IFR ADS-B In system ignore SIL=0 (is true COTS GPS) is because of concern about what GPS source issues could dobtontge system.

FLARM for example manages their system by using specific GPS chipsets and lots of knowledge. FLARM is *not* COTS. You cannot just connect any old GPS received to a FLARM, for good reason.

The development of TSO-C199/TABS was specifically to allow COTS type GPS sources to be used in ADS-B Out systems. To reduce costs, by simplifying some requirements and providing simpler approval processes for devices. A whole slew of organizations including TRIG, FLARM, MITRE, the SSA, and the FAA has input into TSO-C199/TABS. It is a five deal and early products like the TN72 exist. But the FAA never delivered things like regulations to allow installation in certified gliders. Issues like seeking a solution for that are where it would be more useful for the glider community to invest effort.

And again for the airliner scenario here, ADS-B is a red-herring. Stick a transponder in the glider, problem solved.