So if a new monetary system is set in place after a financial collapse and they start to issue CBDC, do you think exchanges will accept them and open markets where they are paired with cryptocurrencies?
I don't see any reason why they won't because centralized exchanges are already accepting fiat deposits/withdrawals direct from/to bank accounts and other applications.
What type of effect would that have on the entire cryptocurrency market?
I don't think it will affect cryptocurrency usage that much. It will probably compete with all centralized stable coins and the so-called crypto of the banks XRP.