FFT style quests where you go into an old dungeon with an objective. Similar to what you do sometimes in story quests (including the one that just released). Quests would also unlock guild furniture, cosmetics, mounts, etc and do not require a free company house to purchase. Once the items are unlocked, every player in the free company is able to purchase them through gil (additional gil sink) and most are unable to be sold via marketplace. Other rewards can be experience, materia, tomes, food and various ship parts. You should also be able to gain relic rewards like light from these quests (to encourage older content and to facilitate groups helping others).

Along with that I would propose the following:
-Free company credits are obtained via the quests above. Previous credits obtained using other methods are reduced.
-Company actions are now consumables obtained via completing quests above, additional actions are added and there are no longer separate grades but the actions can be stacked multiple times increasing duration and potency.
-Free company housing can no longer be bought with Gil, instead require company credits and can only purchase one house plot. This reduces the amount of players buying multiple properties as credits are now mostly earned through a longer period of time and require multiple people.
-Any player in the free company would be able to form a party of the required number.
-Starting from ARR dungeons, SE can eventually include higher level dungeons, 24 man dungeons and bosses.