I'm wondering under what laws they intend to limit ammunition. My reason for saying so is that the SCOTUS ruling under which the restrictions are being modified involve "right to self-defense." I might maintain proficiency with 50 rounds a year, but it might take someone else 50 rounds a month for a few years before they feel proficient. Any incursion on this number could easily be presented as an un-Constitutional restriction against the right to keep and bear arms.
The arguement is of the "where do we draw the line" type. It's arbitrary and varies from individual to individual. The only logical point of demarcation is 0 rounds, but that's synonomous with depriving people of their 2A rights entirely.
"Ok, people. You may now keep and bear arms. However, you may not own, borrow, use, keep, bear, or practice with any bullets. Sorry!"
I wouldn't even venture to guess what a "reasonable" number of bullets per month might be. Many months I buy zero. One month I bought around 500.
I would submit there are no reasonable limits, even though California has gotten away with limiting it to just 10 per clip for years.