It's not quite like that, Ross. The FAA has not changed the spec, first of all. The fuel standard is still ASTM D910 and the engine test plans developed during PAFI 1.0 are still used. What is different now is that both the FAA and fuel suppliers have learned from previous mistakes.
The PAFI entry standards are now stricter than ever and include more materials testing so that the previous mistakes aren't repeated. This will keep out fuels that just don't have what it takes to be a "drop in" for 100LL. Is it challenging to meet this high standard, absolutely. Is it impossible, absolutely not.
The real question is whether the regulators and pilots will have the patience to wait for a proven answer or throw caution to the wind. Time will tell.
I am not aware that any of the original or current formulations met the specific gravity spec. Did/ do any?