These are two separate ideas that are currently combined in one app. By teasing out the data collection aspect, I think you can enable several of the ideas requested:
** Using hard drive space for longer/unlimited capture
A file is a natural separation between these two activities. Reading from a file as it is written is well-supported on all OS's and should not significantly change the interface from the existing viewing logic (which was presumably blocking on more data from the USB port).
** Automatically feed exported data into custom script
By not requiring the UI aspect for data collection, unattended and scripted runs become simple, first-class citizens.
** SCPI capability or user API
The user API aspect of this request is functionally similar to the previous point. Given an API a SCPI compatibility layer could possibly be developed, though their interface doesn't map that well onto the average use case of the Saleae IMHO.