With the current amount of content that is delivered, the patch cycle should be on a monthly basis and even then it wouldn't be that much.

Now what would keep casuals like me entertained ?

Keep the gear tier pacing as it is currently, new tier every 8 months, one new ultimate every year capped to 2 every expansion. Couldn't care less about that since the only interesting thing about gear in this game is the glamour part.

Forget about the current "dungeon" formula, it's boring as fuck and a waste of resources/creativity/talents, replace them with solo msq duty.

New mounts, new glamours, unlockable themed fx and sfx variations of a job skill set (basically reaching out to some modders and entering a partnership with them).

"Open field" area (available week 2 after the release of an expansion) that get updated every month getting bigger and bigger over time, dumping shitload of casuals content in it, roaming bosses that behave like the Rathalos, random treasure chest with actual reward in them (personal loot and stay up 5 min after the first person open it.),

Weather hazard influencing, mobs, bosses, mobility (storm disabling flying and spawning a special boss/event) rare NPC spawn (shop selling cosmetic/minions/mounts, enabling event etc) make the spawn random but make it last long enough so that no one can tell when it'll be available but still allow a lot of people to enjoy it.

Sky island, gigantic subterranean labyrinth (no map but checkpoints that allow you to teleport back and forth to the entrance) littered with traps, bosses, treasures and event (cave in closing some area for a while, floor collapse making you skip part of the map and teleport you randomly deeper in, whether or not you're able to find a checkpoint before getting killed would be up to you) etc ..