I don't think there will every be a fully integrated computer so long companies stay with what they do well. Take nVidia and ATI. If you were to have a fully integrated computer on the motherboard you'd need these two companies either:
A) Getting a processor from Intel/AMD already mounted on the motherboard before they add graphics, then you'd need them shipping it to those companies who deal with sound.
B) They'll be making sound, graphics, processors, etc and putting it all on the motherboard.
Because both of these options would be extremely difficult to accomplish (assuming you want the best quality) add-on cards will always be available. However, you'll still have companies like Intel, who already do a little bit of everything, making these integrated computers for those who are uneducated in the field. There is no way a professional will be working with integrated computers.
Just wait till google buys all these companies mentioned. They will one day rule the world