Having thought about this, with all my vintage full frame lenses, even though there are focal reducers for MFT, the A7iii is my lottery win camera. There's full frame video footage using a Sony and a 60's Helios lens on YouTube and it's amazing.
Neither are bad cameras. 4K 60fps vs full frame loveliness. The deal breaker for many people must be that a year or two down the line, will the market for what they create demand 60fps or not? Like many thought they would demand 3D for everything.
I have some Helios 44 58mm f/2.0 lenses. Very capable of bokeh as you might expect but one of the properties of being a (slightly imperfect) Tessar formula lens is that the bokeh swirls around the edges.
The Pentacon 135mm f/2.8 has the nickname of Bokeh Monster, but is probably rather too extreme for video work.
The local Cancer Research charity shop had a batch of AA battery torches with a bank of LEDs down the side. I bought two, thinking that sometime, perhaps that extra bit of light might come in handy. £3 each.
Late to the party for mirrorless, Canon are still playing catchup.
It seems to be taking the centre of the sensor for the 4K rather than grouping sensor pixels together or evenly taking pixels across the sensor. I can do that as an option on my original model EOS-M in Magic Lantern by selecting Crop Mode as an option. That can be useful with adapted lenses like cine lenses that do not have an image circle that covers the whole sensor. That gives an extra 3x crop factor.