Recently, I went through some of the same focal length envy recently myself. I have a 100-400mm GM which is an awesome lens, but sometimes I want some extra reach. I don't have a 70-200mm so if I moved to a 200-600mm I'd lose the 100mm-200mm range which I don't want to do. Instead, I settled on the 2X teleconverter. It gives me a 200-800mm which I can quickly convert back to 100-400 by taking off the teleconverter. There's always a tradeoff and the maximum aperture is reduced with the teleconverter, but because I don't need the extra reach all that often, it's an easy tradeoff for me to make.
IMO, switching to an MFT system for extra reach is a bit of an illusion. The smaller sensor's "crop factor" makes it appear that you get extra focal length, but it's really just the proportion of the frame vis a vis the subject that changes. Personally, I prefer a high-resolution, full-frame sensor that I have the option to crop to something like an MFT size if necessary. Cameras like the A7R V and A7CR are incredibly versatile in this regard.
This is an interesting topic. Innovation is where the path forward takes a radical course change and progress makes a giant leap ahead. I don't disagree with you about the A6000 being a massive leap forward. It's a little like the Bell X-1, the plane that Chuck Yeager flew to break the sound barrier in 1947. The supersonic planes that have come after the X-1 have long since outpaced its capabilities, but the X-1 was the plane that opened the door to all of the massive advancements that followed.
One thing I think Sony continues to do extremely well is to look to the future rather than cling to the past. I've been in this industry long enough to remember when reps from other companies publicly and privately dismissed mirrorless. As Schopenhauer said (yes, I am brining a 19th century philosopher into a discussion about cameras), "All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident."
I don't have my A6000 anymore, but I I recently got an Alpha 7CR. It's a very different camera starting with being full-frame, but like an F-16 shares DNA with the Bell X-1, the A7CR's lineage can be traced back to the A6000.
Bought an A7CR with a 50mm GM 1.4.
Camera is in full auto and AF settings are out-of-the-box.
I am shocked by these results.
Can anyone help.
Thank you.