I'm struggling to think of an assistant manager, who has become a manager and done very well. Can think of loads that have tried, most United assistants, Shakespeare etc. and some who have got better over time. But its a much bigger skillset and responsibility to be a manager.
Would be well up for having Arteta as a senior coach, assistant manager, but why would he? I don't see him as a leader, he has no experience of management. Would be madness, so seems plausible with current shambles.