My ideas are pretty simple, and involve new monsters in most of them:
- Radscorpions: Those hideous lurking monsters would invade Vaults through the earth (starting concept), and would grab a random dweller somewhere, and drag them to its digging hole.
- Mirelurks: They would deposit a grouped number of eggs inside a vault room without being noticed, so when the eggs hatch... SURPRISE! The sirens start to ring and there you have a new threat!
- Bloodbugs: Those devilish aedes aegypti like monsters would invade vaults, and sting dwellers, making them rad sick, and that would make us make a better use of Science Labs and RadAways. (And that is actually a very good theme to be worked now, since its so... real?)
- Ghouls: A Horde of Ghouls would invade Vaults desperately, sometimes led by A GLOWING ONE! (that would make people want to have their vaults invaded, not wishing the opposite. That would make things more interesting instead of desperate)
- BOSSES: That, in my opinion, would add a nice end game environment. When exploring the Wasteland, dwellers would have a percentage of chance to have an encounter with a World Boss. When a world boss is encountered, a special message would be displayed (in a fixed manner, with another type of colour, showing time the encounter has happened, different from normal messages that disappear after time). Then, a button to enter a place/dungeon/maze/whatever you would name it would appear, and players could decide if they want to fight the boss, within the time of available exploration (until they do not reach 100 items limit or die). If they reach the 100 limit or die during exploration, the button disappears. Since i don't know about the mechanics of this game (coding), the place/dungeon/maze/whatever you would name it would probably have to be separated from "Vault world", because some sort of background would have to be made, to add a better experience when fighting bosses. A Mirelurk Queen for example, showing as background a dirty cave with lots of brain fungus on its sides, and eggs. The fight mechanics i have not thought about, but i certainly think you guys would find a nice way to sort it out. Then it would add a nice hook (possibility) of you guys doing normal dungeons, that any player could access, or "seasonal" dungeons, that would only open during a time of year (christmas dungeon to fight a christmas boss), or even some kind of "premium" dungeons, accessible only buying an "Event Pass" for example. For each kind of dungeon, you guys could make an special group/kit (clothing, weapon, or a recipe) of items acquired only from fighting that specific boss, as a reward.
These are my ideas, i hope you like them! (once i saw someone on forums talking about evicting/banishing dwellers, and that actually became part of the game content, so, why not sharing some ideas for benefit and fun of everybody? )