It surely depends upon what you are trying to say. "Incredibly commonplace" seems to mean that you find it impossible (or, at least, difficult) to believe that the thing in question is actually "commonplace". If that's you're intended meaning, then that is presumably a correct use of the (proper meaning of) the word.However, I'm still trying to explain, with an alternative definition, of how "I can't believe (it's incredible) you just said that" is something better than an 'informal' (i.e. wrong) meaning and so "incredibly commonplace" would be acceptable and not just mean 'very'..
However, I think the 'common usage' (of incredibly) is to mean "very", or probably "very very", and that is the 'informal', not 'proper' meaning. Consider the following examples, all of which I would say represent very common usage .......
The chance of one ticket winning the Lottery is incredibly small
Even the nearest galaxy is an incredibly long distance away
A neutron star is incredibly heavy in relation to its size
Top snooker players have an incredibly high level of skill
The food in this restaurant is of incredibly high quality
etc., etc., etc. .....
In all those cases (and millions of others like them), "incredibly" is being used to mean "very very" (i.e. the 'informal {aka 'wrong'} meaning), with not the slightest suggestion or implication of any disbelief in, or difficulty in believing, the truth of what is being stated. Do you agree?Even the nearest galaxy is an incredibly long distance away
A neutron star is incredibly heavy in relation to its size
Top snooker players have an incredibly high level of skill
The food in this restaurant is of incredibly high quality
etc., etc., etc. .....
See above. If the meaning is "I do not believe [or 'find it difficult to believe'] that such a thing has happened", then I think that is a 'proper' use of the word. If (more likely) the meaning is that "it is surprising/amazing/astonishing that such a thing has happened" (the implication being that one accepts/believes that it has happened) then, yes, I think it would be an oxymoron, and 'wrong'.Is "It's incredible that such a thing has happened" merely totally oxymoronic and wrong?
It doesn't, but definition 2.1 ("very good") does.What about definition 2? It doesn't say informal.
Kind Regards, John