I might be a little lost here, but are you suggesting a way of re-wiring the pack on the fly to switch between 4x 18s modules of 72v (74v?) to a configuration of 72s and 295v? It would be a strange approach if you are trying to simplify the wiring.I might be way off but 72v x4 parallel for charging, bms, dc/dc and then series over to the controller.
As for lumping a bunch of other stuff into the BMS, I am not sure how that would make things simpler for you. The BMSes only real job is to monitor the cell level voltages, balance them if they are drifting, and raise alerts over CAN bus to shut down any process that threatens to over or under-discharge a cell. The BMS pulls tiny amounts of power from the pack, so if it included a DC-DC converter, for example, you would have to wire it separately anyway.
Since DIY EV cars are so diverse, there will probably never be just one integrated system like you are describing - there are just too many variable for something like that to make sense. If you want to integrate a bunch of information into a single display, including GPS navigation, you would probably have to look into getting a tablet that communicates with the BMS over CAN. You can get CAN-USB interface units, but programming something like that, and making your own GUI for the tablet is going to be a big project.