Personally I doubt there's enough of a market to support so many different and incompatible FF mirrorless systems
I do not think so. Thanks to mirrorless, the production costs will be lower than with DSLRs, so you can offer it cheaper and more people will buy it. Same for the production of FF sensors. The economies of scale will be huge compared to the time before Canon and Nikon entered the market for fullframe MLU.
I do not believe that Olympus will offer fulframe. At least there is no rumor about it. Panasonic has a lot more money to offer this parallel to its MFT system. Last but not least you have to bear in mind, that Sony has a 25+ % stake in Olympus. I guess Sony is the largest shareholder of Olympus. I do not think that Sony wants Olympus to enter the FF-market. They can not forbid it Panasonic, but they will not allow to make the position of Panasonic even stronger by allowing Olympus to offer FF too.
Thanks to Smartphones, more people than ever get interested in photography. As soon as products will be available, which offer the same convenience to share images at an affordable price and good lens selection, more poeple will use it additionally to their Smartphone.
Nikon dropped the 1 series
Yes, but Nikon failed to develop the system so that it offers a significant advantage to use it. I used to have the Nikon 1 System. I loved it. But lenses were as big as MFT lenses, some even heavier and Nikon failed to set the prices low enough to get better volumes to sell. Same as now with the Z6/Z7, Nikon still tries to protect its DSLR business. They do not understand, that if they do not do it, others will do and get the money.
I do think MFT and fullframe is an ideal combination side by side from the perpective of a producer. Large enough steps inbetween regarding image quality and portability. Fujis attempt with APS-C and Medium Format is more risky, since MF requires a lot more money and the sizes are significantly bigger so that for the majority of photographers just for the size alone, it does not make sense.