The SQL Server fallback feature is flexible enough to support a fallback strategy relating many primary servers to many fallback servers.
Plausible means of implementing fallback are becoming available through specialized hardware and operating system features. Major vendors now offer specialized hardware that is capable of automatically shifting the control of a "switchable" hard drive array from a failed primary server to a fallback server. For example, hardware can be configured with one separately housed hard drive array connected to two computers. Only one of the connections to the hard drive array is active at any one time. The other hard drive connection becomes active only if the system detects that the computer currently in control of the hard drive has shut down because of a hardware or operating system failure. Detection of such failures is made possible by a direct connection between a COM port on both computers, over which "heartbeat" signals are continuously transmitted. The automatic process can also invoke a user-written program on the fallback server when the hard drive array is switched to the fallback server.
This type of automated fallback hardware configuration allows one fallback server to support one primary server. Contact your hardware vendor to verify that your hardware can support this fallback option.