SDI can't do any communication between the source and sink. You can do a limited form if you use two SDI cables (one upstream, one downstream) which is what stuff like BlackMagic's bi-directional micro converter does, but IIRC that's only used for talkback to the camera operator and HDMI CEC messages which is how they implement things like their ATEM Mini consoles triggering recording - not for DDC-style format and framerate negotiations.
Also, device manufacturers don't do SDI on consumer devices because SDI is by definition unencrypted and uncompressed, so it's at odds with HDCP.
BMD has done some innovative things through their SDI port, specifically enabling camera control with an Arduino-add-on board.
Someone finally did what I've wanted to see for years: built a follow-focus unit that controls the focusing motors in the lenses, so you don't have to bolt a ridiculous contraption (and janky focusing-ring adapters) onto a lens to turn its (non-mechanical) focusing ring manually.
What I want to see is someone dump the FPGA in these Micro Converters and hack it to add an USB interface. The Micro Converters are all just the same in the interior: SerDes units and clock/redrivers on the I/O ports and an FPGA that additionally has an USB connection which is used to power the converter but could also be used to do other things.
That FPGA should be powerful enough to do a lot of interesting things - anything from fooling around with commands (like with the Arduino board) to image manipulation (e.g. a watermark embed).
Also, device manufacturers don't do SDI on consumer devices because SDI is by definition unencrypted and uncompressed, so it's at odds with HDCP.
[1] https://www.blackmagicdesign.com/products/microconverters