One of the motivations for dispensing with a flame diverter and trench was that no such facilities exist on destinations such as the Moon and Mars, from which they will eventually want to launch return missions. If they can demonstrate that Starship (without Super Heavy, which is only needed for launches from Earth) can operate from unimproved terrain, that means they don’t have to find a solution for that chicken and egg problem. We now know that “size matters”, and while Falcon 9 can land with one engine on a flat concrete pad with no problems, a 33 engine Super Heavy won’t work. We’ll still have to see how Starship fares on its own.
NASA, in conjunction with Masten Space Systems, was researching a concept called “in-Flight Alumina Spray Technique” (FAST), in which a lander hovers above its landing location while injecting aluminium pellets into the rocket exhaust, where they are liquefied and sprayed onto the surface, creating an instant landing pad where the lander sets down. Unfortunately, on 2022-07-21, Masten filed for bankruptcy after running out of money trying to fulfill a NASA Commercial Lunar Payload Services contract on which they admitted to “grossly underbidding”. I don’t know if anybody else is pursuing the FAST concept. Here is a video about the idea.
One of the first things that will have to be done in establishing a Moon or Mars base will be constructing a landing site for subsequent landings with a surface that doesn’t spray debris in all directions and a berm surrounding it to retain any regolith that does go flying. A lunar lander can eject dust at velocities sufficient to enter lunar orbit and possibly damage spacecraft in orbit, not just sandblast anything in the vicinity.