* do you think it important to remove all locking?
There are certainly cases where automatic locking would remain useful.
* would you be satisfied (or put up with) having to
explicitly opt-out of locking when opening a file?
Yes.
* do you see any value at all in locking by default to
catch bugs where files are read and written concurrently
by accident?
Yes.
The use case whose current behaviour surprised me, was when I wanted a single writer and multiple readers. I did think that was what the standard allowed, but I was mistaken and it turns out that you get single writer *or* multiple readers.
The case for multiple simultaneous writers is harder to make, but it should be possible. I agree that having the unsafe behaviour be the default is probably unwise.
Regards,
Malcolm