iRule to process URI and Header data groups

Apart from adding the hostname and path in your datagroup, you could use other datagroups to handle that... Untested, but perhaps something similar to this:

when HTTP_REQUEST { 
    set hostLower [string tolower [HTTP::host]]
    set pathLower [string tolower [HTTP::path]]

     Use a datagroup matched on the host name that will give you the name of another datagroup to use to look up the pool redirect
    if { [class match $hostLower starts_with dg_host_dg_lookup] } {
        set dgName [class match -value $hostLower starts_with dg_host_dg_lookup]

         Now check the correct datagroup for the path
        if { [class match $pathLower starts_with $dgName] } {
            pool [class lookup $pathLower $dgName] 
            return
        } 

         If that didn't work, check for the header value
        if { [HTTP::header exists remote.contenttype] && [HTTP::header remote.contenttype] equals dg_header_pool_redirect } {
            pool [class lookup [HTTP::header remote.contenttype] dg_header_pool_redirect]
            return
        }
    }
}

You'd need to add additional data-groups for each host (which includes the hostname:port)