VPC will only become obsolete if there exists a method to switch from OS X to Windows and back without rebooting your computer (preferably even keep applications running when not the focus OS but that is not required). If VPC runs at >60% native speed it will serve the purpose for people who have to use Windows apps from time to time but don't want to have to reboot to surf the web or check email (if I set up my next Mac to dual boot, Windows will only use the net for updates to avoid other problems).
Heck, they sell VPC for Windows so you can test applications on different Windows versions without worrying about crashing your main OS, so why not keep it for Mac? The price is set so they expect to make a profit, it may take money to develop and support but they will still be making money off of it. If they keep it they can convince many Mac users that they need it and make the money on VPC and Windows rather than just Windows.