This is a good question and a genuine concern. I can share my thoughts on it; however, as vantam-subhuman put it, it is too early to have any “knowledge” in this regard.
The banking regulations at present require individual banks to perform KYC - regardless of how many other banks have done that with same person. This is deliberate, not something that was overlooked.
Given that, if a bank where you intend to use ADA knows about your Monero holdings it is obligated to understand what you have been using it for. That is part of the AML (anti money laundering) check. If you are unable to demonstrate that there was no ML, or if the bank is unable to confirm that, then the AML check part of KYC is incomplete and therefore KYC is incomplete.
In that case the bank is most likely going to decline future crypto transactions with you. The consequences to the bank for accepting transactions without KYC are severe. There will be dozens of regulatory fines and the employees involved will receive stiff penalties.
As for metadata attached to ADA transactions; that’s the easy part. I’ve heard Charles mention this in a few talks. This can be done via smart contracts that
take all identifying information about the entity that wants to enter the regulated financial market
Perform automated checks - how this will be done in unclear to me at present
Encrypt the metadata such that only the concerned authorities in the jurisdiction involved can read it
Make the transfer to a fiat or ADA account in a bank via some bridge crypto (like Enterprise Cardano or Ripple).