Who knows... Latest firmware for 5D3 is realised in 2019 which corrects some vulnerability issue, why not include some minor changes like EC mode if Canon decide fix another vulnerability issue.
I am really still not understanding why canon decide to not allowing to compensate at M mode with auto iso turned on, it is simple to add it to firmware. M mode not going to be not manual with EC availability, it will be just easier for some shooting...
