Hi telecastle,
The intended use of PCI Passthrough is for users with high-performance storage or network controllers to connect those controllers directly to the VM which needs it at peak performance. It is not intended for turning a VM into a fully-fledged "client" using the host's hardware. The many and varied quirks of PCI[e] devices mean that we can only support passing through well-behaved devices. The many-more varied quirks of everyday motherboard-integrated or southbridge PCI[e] devices mean that we will most likely never be able to support passing-through such devices. At least standalone/plug-in PCI[e] devices are designed to operate as standalone devices, and we know that they won't have stealthy interactions with other devices in the host, or with the host firmware... we can't say the same for integrated devices.
As a concrete example: If you pass through only your host USB 2.0 controller (00:1a.0) and start connecting/disconnecting USB devices, we can not guarantee that there won't be unexpected interaction with the xHCI controller (00:14.0) which shares the same physical ports. We have no way to characterize what could possibly happen in that configuration, so there is basically no way we can support it.
I've been amazed by some of the reports here of what people have managed to get working by passing-through PCI[e] devices, but I have equally been terrified to hear some of those stories, which are often way beyond the bounds of what we support!
The SMC fix is queued up for delivery in a future ESXi 5.1 update... I can't say precisely when.
Cheers,
--
Darius