Actually GFDI was always required. And the solution of grounding one DC conductor (but not solidly, only through a fuse) was a simple way to engineer that requirement. But it made putting in a transformer necessary, which lowered efficiency, and it wasn't really that reliable. Once manufacturers figured out how to make reliable electronic GFDI that would get listed by UL without using a grounded conductor, transformerless inverters took over quickly due to lower cost and higher efficiency. They are also safer for installation crews and others, if perhaps more prone to nuisance tripping and destructive failure in the case of faults.
I'm not sure when GFDI was first required, my NEC library only goes back to 1999, but up to the 2008 NEC it was only required on roof mounted PV systems on dwellings. I designed a lot of roof mounted commercial systems without GFDIs and no ground mounted systems needed them. It took several years for inverter manufactures to catch up after 2008 went into effect and they started putting GFDIs in the larger inverters. Up to then it was only standard on residential inverters and those were too small for commercial systems. It was questionable if GFDI was required on apartment or condo buildings and a lot of those from that time don't have GFDI. The systems were solidly grounded at the inverter DC input with a bonding jumper, but without GFDI you could do it anywhere in the array if you wanted. Good times.
I'm not sure what you mean about electronic GFDIs. Some inverter manufacture tried to get an allowance for an electronic switch to act as a GFDI several NEC versions ago but it was voted down by the CMP. The usual way to comply with 690.35(C) in an ungrounded transformerless system is to shutdown the inverter when a ground fault is detected.