IP core business model

I endorse what Keanu13 has written. There are successful companies out there selling IP cores, although the most successful of these are mostly selling into the ASIC/IC markets, for example the MIPS ARM core.

Companies increasingly look to outside suppliers to provide proven IP cores, for example SATA, HDMI, USB, PLLs, ADC and DAC, leaving them to concentrate on their core expertise. The same is true, but to a lesser extent, for FPGAs, (note the cores I mention above usually have an analogue component, but digital only cores are also sold, e.g. I2C, NTSC/PAL encoder/decoders, audio sample rate converters etc.).

If you are looking to provide IP cores for Altera FPGAs the most important first step, (after designing the core), is to obtain the encryption software so your core cannot be copied. You can then set the parameters on that encryption, length of time, machine specific, device specific etc.