The main risk factor is people trying to pump too much juice into a wall socket rated for a lesser current. Plus the connector needs to be male - shock risk. The combination of live and male is not generally something you see in households and people may not register that it’s something outside of normal household risk profile.

That plus bit of risk of things being energised that say a lineman thought would be out. This can be mitigated by using systems that only feed in when they sense it’s connected to the grid

Linemen will always ground a transmission line before doing any work on it, unless live work is authorized, and then other safeguards apply. They never assume a line is actually dead just because it's supposed to be dead; they always assume there might be a backfeed or other source of potential on the line.

The balcony solar rigs (at least the properly designed ones) don't energize the male connector until they detect that it's plugged in. And they de-energize it if the mains/utility power goes out.

Those risks are covered.

https://www.gov.uk/government/consultations/plug-in-solar

> This can be mitigated by using systems that only feed in when they sense it’s connected to the grid

Which are the only ones that are legal.