£2 to £2.50 would be a significantly less big jump than £2 to £4.10, which is my current non-capped fare...
It's also important to remember that in some circumstances, those who are still paying cash are those with least money and most need to budget (there is anecdotal evidence to suggest this in multiple areas of payment, not just for bus fares), so asking people to go back to finding 10ps and the like will not be helpful. Keep it to as few coins as possible. I recall being told some years ago that cash is not there to help you spend, it's to stop you from spending: unlike plastic, when you run out of the physical thing, you can't keep using it.
Ultimately, this was introduced as a "help for households" measure, not a public transport improvement measure, and I think all the other "help" measures have now been withdrawn. Even as a non-driving (never learned), full-adult-fare paying customer, I accept it can't continue forever.
What is needed now is a clear plan that the government stick to, and not suddenly withdraw or extend when and if they find a few more pounds down the back of a Westminster sofa. To paraphrase the leader of Kent County Council yesterday, without knowing what is happening, bus operators cannot plan. I think the DfT needs to set negotiations in chain now with operators for a £2.50 fare cap between January and June 2025, then £3 June - December 2025 (as I believe was originally planned for 2024), and then consider the future from there.
After all, it was meant to be a fare cap, not a permanent fare undercut. (Yes, I know, like speed limits they are often driven to rather than under, but the principle of the name applies!