This is a topic very near and dear to my heart.

What I've found in my mullings and musings is that this is a problem inherent to "level" as it had historically been implemented. Sure, it can simplify calculations, but I'd argue for it being the biggest factor in the switch between the growth and maintenance portions of the MMO life cycle, and it can make that switch for you if you don't plan ahead very carefully.

The solution I've been contemplating is just not having a typical level system, or at least keeping it behind the curtain, rather than putting it in front of the player as THE carrot to chase.

Consider having more avenues for meaningful horizontal progression that present themselves early to help de-emphasize vertical progression and you may find yourself forced to compete with inflation less often.

Level and equipment limits are the norm.

Quickest example, racing games. This is the racing MMO business model I've seen duplicated.

you'll have level 1 cars for 3 months, level 2 cars for 3 months, level 3 cars for 4 months, etc. This way the players purchase the new cars every time, and the power creep is controlled. The final might be level 12 cars, with a temporary upgrade which lasts 30 days.

ported to another country, you won't start with the level 12 cars, you start the business model over again with level 1 cars

Games that take months to reach a level cap have bot players, very few humans have staying power, maybe 1/1000 players who are active for over a year will still enjoy the game for just the game, the rest want peers. If everyone is a different level they don't know their peers.

You could also look at WoW, just because they have a level cap for subscribers who'll eventually all level out. I don't have knowledge about WoW beyond that.

This is pretty much the norm, forced team play.

WoW is taking long-overdue steps to minimize the gap between old and new/returning players. With the expansion later this year, they're allowing new players to jump to more recent and relevant content without the long level grind.

It won't be long before this is extended to a full mentoring system like those that several quicker-responding games already feature.

So while yes, level systems are the norm at present, they are starting to show serious wear. I wouldn't count on them being the norm too much longer.

Sorry, wasn't available for few days due to computer upgrade, thanks to all contributing

This is a topic very near and dear to my heart.

What I've found in my mullings and musings is that this is a problem inherent to "level" as it had historically been implemented. Sure, it can simplify calculations, but I'd argue for it being the biggest factor in the switch between the growth and maintenance portions of the MMO life cycle, and it can make that switch for you if you don't plan ahead very carefully.

The solution I've been contemplating is just not having a typical level system, or at least keeping it behind the curtain, rather than putting it in front of the player as THE carrot to chase.

Consider having more avenues for meaningful horizontal progression that present themselves early to help de-emphasize vertical progression and you may find yourself forced to compete with inflation less often.

I think key element is giving chance to progress horizontally as you mentioned.

I consider adding multiple "careers" people can chase (but Killers will not be happy) and also consider a "technology" feature hopefully protecting both parties.

If you really get down to brass tacks, the "killer" style of gameplay is kind of incompatible with the MMO genre anyway.

Approaching a long-running game with as a player focused on very short term and impermanent goals seems like a recipe for disappointment. That's not to say that MMO devs should not be consideting this audience, or that some accommodations should not be made for them; just that giving that sector too much weight in design decisions probably isn't wise.

I would contend that this is a big problem with, in particular, WoW's philosophy, and that it has poisoned the player well to an extent. Blizzard's unwillingness accept the depth of the disparity between PvE and PvP has plagued them for years, and has been a major contributor to the discontent a lot of their playerbase feels.

Look back to what they did right in the beginning to make the game so popular. Be willing to look at MMO norms and ask yourself if they are the best way to do things, or just the familiar way. Don't be afraid to rattle cages that need rattling, but mind that you don't fall into a "witch hunt" mentality.

My random top-of-my-head thought is to decentralise power. For example, players can create towers/magic circles/whatever which are only usable within a certain radius. A rich long-term player can have lots of them, so it's quite safe for them to walk from area to area. However if a new player builds a good one in the same area as an old player, they can fight on relatively even terms. The old player has a certain disadvantage that they can't easily watch over all their territories, so are open to challenge by newcomers. Another angle would be encumbrance limits or skill trees that have exclusive branches. The old player has a huge bag of tricks, but needs to pick carefully which ones to bring to a fight.They may have discovered nearly everything, but cannot access everything at once.