.......aside from that I said the problem is if banks just stop issuing accounts to US citizens because they don't want to comply with this, that would be an issue.
Yes, that would be an issue. As I said earlier in this thread, right now, we don't know what the banks/building societies are going to do. If a building society is trying for a 'deemed compliant' status, one of the stipulations they must agree to is to allow Americans to have an account.
The UK has signed a 'Model 1 IGA' (Intergovernmental Agreement). Its express purpose is to get around the UK data protection laws and allow the banks, via HMRC, to give the financial data to the IRS. Switzerland has signed a 'Model 2 IGA'. The Swiss banks give the account info directly to the IRS with the Swiss Councils blessings. It is now very difficult for an American in Switzerland to open a new account, with only 3 or 4 of the largest banks allowing a new account. If the same happens under a 'Model 1 IGA', it would indicate a grave problem for FATCA.
As for renunciations, watch for the figures to continue growing. More and more people around the world are becoming aware of 'US Person' status. Those who have no ties to the US may find renunciation a more palatable solution.
Of particular interest (and here in the UK possibly more than other countries) is the 'Accidental Americans'; those who don't realise they are, in fact, American and a US Person for US tax obligations.
The plan is for the banks to search their records for 'US indicia'. This includes a US place of birth, other ties to the US (green card for example), or even accounts with regular transactions with the US. The banks will determine the reporting to HMRC based on this (and they can't afford to get it wrong). At the same time, they will inform the account holder that their info will be forwarded to the IRS. As this happens, we may see a number of those Accidental or Unaware Americans seek to renounce.