Multi-drop 100Mbps network?
LVDS as a physical layer will do multidrop into the Gbps.  You might need to roll your own higher comms layers, but iirc Xilinx can supply IP to at least layer 2 go with the LVDS transceivers in their FPGA's.  They also offer GTP transceivers in their higher-end FPGA's but I'm not sure whether GTP supports multidrop.  Also, there are many standalone LVDS SERDES devices, again into the Gbps range, that are designed to do exactly what you want.  Just search for LVDS or SERDES on one of the major electronics vendors websites for examples.