It might be that carrying atmospheric shielding will change how you can exit SC near planets, and that way end up in instances meant to allow you to cruise through the atmospheres and land on the surfaces.
Of course, that may be a non-issue with atmosphere-free planets. In that case, it may be we need a tiered distance trigger. Getting into the shortest-distance trigger zone would mean exiting SC in a landing instance. Which may work well for ships with atmospheric shielding in all cases, but not always well if no such shielding is installed. That way it will be another way Elite can be Dangerous!
And there may be an upper limit for what atmospheric pressure the ships can handle, so that we won't be able to dive into oceans without being the not-forgotten Moray Starboat and won't be able to land on surfaces of planets with atmospheric pressures on the order of 1,000,000 or more (we might be able to land ON the atmosphere though!).

S