So far no word on when it might be possible to use the iOSD Mini with the upgrade board. There are rumors of a "new" new board, or a Y-cable that would provide a CAN-BUS port, but so far that seems to all be speculation.
As far as wiring in the DJI AVL58, it's pretty simple. The TX has an 8-pin cable that terminates in two connectors: a Deans style battery connector and a 3.5mm 3-conductor plug. Depending on how "neat" you want to keep your installation, you can either cut those connectors off, or install mating connectors on the upgrade board, your choice.
Whichever method you choose, the battery conector can be soldered to any VCC+ and GND on the main board -- either on one of the ESCs or at the point where the main battery leads connect. Be absolutely sure you solder this *perfectly* as if you end up with a cold joint or a loose connection, you will be causing your entire quad to lose power during flight.
For the video connection, the tip of the 3.5mm plug is 12V+; you don't need that. The video signal is on the middle ring, and the GND is on the sleeve at the base. If you want, you can just solder a 3.5mm plug to the end of the thin cable that comes with the upgrade board. Solder yellow to the middle ring, brown to the sleeve/base, and don't connect the third wire (it's 12V+). Then just plug in. Alternatively you can cut off the 3.5mm plug and solder the wires directly with no jack.