While you are correct in your assessment it seems that you forgot that is going to take more than one century for all bitcoins to be mined, and it's very unlikely that any of us is going to be around by that time, however as bitcoin becomes more difficult to mine and more bitcoin is lost because people forget the password to their wallets we're going to see a decrease in the supply and that will make bitcoin even more valuable.
I think there is no limit for bitcoin to be mined. When we want that bitcoin will be the global currency in the future then mining process will also never end. It will continue till the end of the world like other paper currencies.
I dont believe that 21M is the last limit for bitcoin mining. Anyway if a company produce lot of items but there are no buyers in the market they cannot make any profit.
I'm sorry to say this to you but that is the limit and that limit is never going to be increased, the developers are never going to propose it because they understand that the reason why bitcoin is so valuable is because it is scarce and if they change that then bitcoin is not going to be that much different from fiat currencies.