More to the point, we effectively need it to vary from user to user, although I understand why that is not an ideal situation.
- As @deborahgu mentioned, people who are using extensions already have a "non-standard" setup, and browsers compete on user interface which seems like a reasonable thing.
- People with screenreaders tend to have a massive set of shortcuts (pages of them, if you read them as a list).
- People who swap keyboard regularly (e.g. working in a non-latin language and having to do anything so backward as write code that only works with latin characters, or hopping around reading email from other people's computers, or just being used to an AZERTY or a QWERTZ or something because they were born in a large European country) have different shortcuts available depending on what they are doing now.
Effectively web developers should not document the behaviour they expect from the user - in particular because they have no way of knowing if the user can do that, let alone whether it is helpful or causes a crash in a critical system someone has.
Web developers should be identifying things that should have shortcuts, providing a suggestion - that user agents may well ignore, although probably only with a good reason, since it implies extra work - and focus on ensuring that there is a way to know what an assigned shortcut will trigger.
For things with
accesskey set, this would match the "accessible name computation". There is a draft spec, and since 80% isn't necessary it is easier to read than it looks, if not wonderful.