If you go over the transfer balance cap, the ATO will let you know that you need to remove the excess amount, plus any associated investment earnings, from your Retirement Income account. They will also apply tax on those earnings. For a first breach, you will be subject to 15% tax, with subsequent breaches subject to 30% tax.
You will not be considered as having gone over the cap if your Retirement Income account balance grows to more than $1.7 million due to investment earnings.
If you're concerned that this limit might impact your retirement plans, you should seek financial advice.