Not much love from sony for a-mount these days?

Google is your friend: NEX-VG900 is already a fullframe nex camcorder with e-mount. The e-mount CAN handle fullframe. They made it future proof, so to speak.

However it's true that current nex lenses are meant to cover the APS-C imaging circle. But there's theoretically nothing preventing them from making e-mount lenses that cover the fullframe image circle. All they need to do is a design where the lens has some vacuum between the rear element and the sensor, in order to avoid extreme ray angles caused by reduced flange which would badly harm the FF image corners.

Nothing technically impossible here.