Build software in NIOS II using sopcinfo file without using any board

To compile a Nios program you only need to know the offsets of all the hardware items.

These could be defined by your own specification document and the fpga image and code both built to match that specification.

The integration between the fpga design and C code might help beginners - especially on courses! But in a corparate environment the software and hardware are likely to be designed and built by different people - often in different teams.

Once a method of downloading the code that doesn't require JTAG is working (and most systems will have one - if only because you want to be able to field-upgrade the software and probably the fpga image), software development can be done on systems that don't have any of the Altera tools installed.