Communication fabrics connect large numbers of processors and peripherals. Many fabric technologies are available, some of which can be applied to MCUs featuring high-speed interfaces.
For example, RapidFabric works with existing Serial RapidIO-based MCUs. The RapidIO Trade Association handles the definition of RapidFabric along with Parallel and Serial RapidIO.
PCI Express fabrics are unlikely. Advanced Switching Interconnect (ASI), though, which is based on PCI Express hardware, is probably how PCI Express MCUs will link together.
Stargen's Merlin AXsys ASI switch connects to ASI nodes as well as PCI Express nodes. It uses tunneling technology to link PCI Express nodes to other PCI Express nodes. ASI nodes can also access PCI Express nodes, but the switch handles the translation between ASI and PCI Express protocols. Still, PCI Express is a host-based architecture, and ASI simply maps one or more PCI Express hierarchies on an ASI fabric.
HyperTransport isn't currently defined as a fabric. Its original target was as an on-board chip-to-chip interconnect. It excels in this environment, but designers push the limits with ever-larger HyperTransport systems.
InfiniBand is one high-performance fabric interface that's unlikely to make it onto the processor itself. This is due more to the kinds of processors being used with InfiniBand systems. Chips like Intel's Pentium or Xeon tend to be rather large and power-hungry.
Adding an InfiniBand chip is relatively minor compared to the rest of the support structure, including chips like a South Bridge and memory. InfiniBand also lacks the broad support of Serial RapidIO and ASI technologies.
Ethernet is the original fabric, and the first fabric delivered with backplanes such as the PCI Industrial Computer Manufacturers Group's AdvancedTCA. Gigabit Ethernet is the mainstay at this point, yet 10-Gbit Ethernet remains the holy grail in this fabric. A few MCUs have Gigabit Ethernet, but don't hold your breath for on-chip 10-Gbit Ethernet.