I see what you mean and concern now. Sorry for confusing issue description. I'm not intending to modify QUOTED identifier.
Let me explain more. My thought is just making IDENTIFIER into LOWER(IDENTIFIER). This is the way of PostgreSQL.
In short, every database/table identifier without quote should be handled as LOWERCASE one. And, in that context, '\d table1' equals '\d Table1' and '\d TABLE1'.
Isn't it? Hyunsik Choi.