To close my own thread... I called Swiss:

- One more ticket is available for sale
- No seat is free for selection in the ”public” system
- 2G is always blocked for SEN/HON and this is the seat that I will get if I book. It is the only seat available on the flight I am looking at. Similarly, on another date 2D is shown as the only free seat in the public view, but 2G is then actually also available.

When logged in as SEN, 2G is not shown to me as available for selection, so perhaps the call center agent should have said that it is HON block rather than SEN/HON block. I wonder if an HON would actually see the seat as open for selection directly, or if one always has to call. These days most companies try to push as many interactions as possible to online channels, but apparently not Swiss.