It's worth noting that SIMBIDS was a cost effective technical retrofit solution that cash strapped BR devised and used in the 1980s/90s. It allowed a basic but safe and useful signalled bi directional facility to be provided through existing relay controlled areas for pre-planned and emergency use, avoiding the difficulties and delays associated with working by pilotman. Lack of AWS with suppression for the reverse direction saved countless wires, relays and cables in that generation of equipment. There were other quirks. Auto signals in the normal direction didn't replace to red for a reverse movement, and there were no separate telephone circuits for the new reverse direction signals. The simplicity meant SIMBIDS was cheap and fast to build and commission.
It's not necessary or appropriate to avoid full bi-di control standards and train protection in new processor based signalling installations today. With their data-link networks and distributed input/output modules there are no cabling or complexity saving arguments in avoiding full bi-di controls and train protection, even if that was allowed. The question of capacity in the reverse direction is separate and largely down to how many extra signals the client is prepared to pay for, bearing in mind that wrong direction signals are sometimes more difficult to sight effectively and can require more elaborate ironwork than usual to support somewhere visible unambiguously to approaching trains.
I'm pretty certain the term SIMBIDS is no longer referred to officially anywhere in current rules and instructions, but the remaining original localities so equipped are still subject to similar restrictions on use, now written as local instructions for the particular sections. The last of these are fast being removed, as resignalling progresses on the GWML for example.