The Java Library uses int as the type for the index (  https://github.com/iotaledger/iota.lib.java/blob/bac4c728c4d78fc1a6c2907d622c7c064a027f33/jota/src/main/java/jota/utils/IotaAPIUtils.java#L34  ).

The strict equivalent of the Java int is long int in C, which is 2,147,483,647.

But this is only a limitation of the library. The nodes don't need to know about this, so the library could be changed to support bigger numbers, provided that wallets in other languages also support those bigger numbers. Python: sys.maxint = 9223372036854775807

There's also the possibility of using different seeds. Like have an algorithm generate a new seed per month.

The Java Library uses int as the type for the index (source code on Github).

The strict equivalent of the Java int is long int in C, which is 2,147,483,647.

But this is only a limitation of the library. The nodes don't need to know about this, so the library could be changed to support bigger numbers, provided that wallets in other languages also support those bigger numbers. Python: sys.maxint = 9,223,372,036,854,775,807

There's also the possibility of using different seeds. Like have an algorithm generate a new seed per month.