I've seen cisterns mounted on the inside face of the boxing. Some of the modern ones are very compact and light empty. Outcomes are bad if overflows happen but a modern cistern should overflow into the toilet quite reliably which means most householders will notice.
The wall hung equipment is great, not really for the older houses but you can fit/remove a toilet so easily because it's been engineered to work. You would end up giving up around 50mm more than normal concealed to accommodate the frame standing in front of the soil pipe. If you want wall mounted it's the only way.
When you custom mount one you just need to have a method to push the feed to the pan into the connector at the back (i.e. try to design it so you can reach with your hand). Use a long flexi soil connector so you can check it's fixed it to the pan then push it back to the wall.