Bear with me here. I'd be very curious what you all think about this.
Most MMOs out there come with a character progression feature. Your character does an activity, some number in the background increases and your character becomes better. Be it by linear levels in WoW, allocatable skill points, skills that train as you use them (e.g. Ultima Online) or passively trained skills akin to EVE. All of these systems and games are vastly different, but they all have the growth of a character in common.
On the other hand, there have been games where no character growth is present. Openly sandbox games like Second Life, where the sense of "progression" comes from building social connections. Exploration driven games, where you learn about the world, but the character stays the same. Or games like Star Citizen, where your "progression" is largely measured by wealth and player skill.
My question is this:
Suppose you have a social MMO. You harvest, craft, claim land and build. You form guilds, grow a business and work on large community milestones. The crafting has a player-skill component to it, so you as a player learn how to do it better, which ingredients work best. You learn about trade routes or how to optimise your NPC run factories. Clearly, there is progression going on. A player starts as a nobody. Looking back at your early days, 3 months into the game, you will see turning from a street urchin to an owner of a powerful trade empire. Your position in the society moves up.
But there are no levels, no skills that your character increases. You get better by understanding the systems better, and by owning more stuff, but a 1-year-old veteran character will craft the same item as a fresh one (provided you use the same crappy process).
Will the lack of numerical character progression be a deal breaker?
Would players leave the game, because there is no number reminding them that they are progressing? Would players get confused, because after a play session, they can't point to a number and say "Aha, this is what I did today. I can't wait to push that further tomorrow!"