The all-Type-C hub is certainly possible, and eventually will dominate. Examples of "Hybrid-A-A-C-C = >C cable" hubs do exists.
The main problem here is in additional cost of Type-C port. Also, the purely C hub is largely useless these days, since the number of devices with Type-C connectors is still miserable on the market.
The Type-C port must have the polarity-detection mode, lane muxing, and full VBUS power control, because the VBUS switching (must be always OFF when no cable is attached) is mandatory, in contrast with the regular USB, where "ganged" wiring of VBUS is allowed. Even in classic USB the hubs who implement full power control on VBUS are selling in $40-$50 range.
Until design houses as GL, VIA, TI, or Microchip came up with hub ICs that natively support the lane muxing, CC detect/handshake, and VBUS control, the C-C-only hubs will be expensive to make, and therefore harder to find. Enhanced Power Delivery increases the cost dramatically. But I guess this all is a matter of time.
Bi-directional hubs are not possible in principle, the USB was designed as host-centric architecture with star topology, where hubs are expanders of the preconceived topology. Hubs are not a set of wires or switches/muxes, they cannot "interrupt" any OTG negotiations. A USB hub is a pretty sophisticated communication processor, which has a local and independent port control management, with deep elasticity buffers, with re-timing and re-sampling of data flows between upstream port and downstream ports. But they can't route anything from one downstream port to anther downstream port "across" the hub.
Theoretically, however, it is possible to design a device (SoC) that would have multiple OTG/DRP ports, where the CPU would provide any type of cross-communication, but this will be a new type of USB device, "super-hub", or "super-dock", or something.