The PCI slot soundcard can still be the best performing and most reliable option for recording audio into a computer. If this was not the case soundcards based on this bus design would have been completely displaced by USB or Firewire alternatives long ago.
Companies, in their rush to create new product lines, have really been steering the pro soundcard buying public towards firewire-based audio products. But there can be some real nasty firewire controller chip issues to deal with if you go down that road. Texas Instruments firewire controller chips have proven to be the most reliable alternative, while some people experience functionality problems with VIA firewire controller chips. The kicker is that many people opt to use on-the-motherboard firewire ports for connecting their firewire-based soundcards, and, unfortunately, most motherboard-based firewire ports use VIA firewire controller chips. I imagine these potential firewire issues will be addressed as new motherboard designs with more reliable firewire controller chips arrive on the scene.
USB has always suffered a bad rap, due to the limited bandwidth of USB 1.0. I don't think that USB 2.0 suffers the same problem, but many soundcard companies seem reluctant to embrace the standard, for reasons unknown to me.
The soundcard manufacturers seem to be dragging their heels on PCI Express-based cards also. I think maybe PCI Express has some issues with providing large amounts of reliable 3volt and/or 5volt power to particularly demanding bus-powered devices, due to the narrowness inherent in the bus design. Just a some-what educated guess here.
So...if I am correct, the PCI slot soundcard still makes for the most risk-free audio rig, and because of this alone it will probably be around for quite some time yet.