It's no secret that Marvel's Avengers has been far from the big success that Crystal Dynamics and Square Enix may have hoped for. Designed with a full singleplayer campaign and a multiplayer-focused endgame intended to give it a long tail, Avengers was halfway decent but simply didn't have enough there to maintain players' interest.
Personally I found the endgame got very boring, very quickly. As part of the game's next major update, which sees Hawkeye arrive on March 18 (another problem with Marvel's Avengers: the DLC so far has focused on the most boring characters), the game's levelling system and loot is being completely reworked. And it's being changed in a manner that suggests the future for this game—as has seemed inevitable for a while—may be free-to-play.
A blogpost innocently titled 'Upcoming Cosmetic and XP Rework' has the task of explaining to current players who've paid for the game why things are about to get a lot more grindy. It begins by saying that the current levelling curve is not really a curve, and players level at a steady rate, so brace yourself: "This has led to pacing issues, such as skill points currently being rewarded too fast, which may be confusing and overwhelming to newer players. We want each decision to invest in a skill or Heroic to be more meaningful."
This does not align with my experience of the game at all, and I doubt many would agree with the above. In fact Avengers as it stood already had something of a grind to it, whereby you earned basic skills for each character relatively quickly, but then had multiple subsidiary skill-trees to sink extra points into and customise your playstyle. This change will increase the amount of XP needed to level up "starting from around level 25. This amount will increase the closer you get to level 50 so that it will take longer to reach higher levels, and will only affect character level, not power level."
So... that sucks!
In addition to this, the in-game cosmetics, long a bone of contention among its playerbase, are being reworked. The post is not crystal-clear (b'dum tsh) about exactly what's happening here, though says "the goal [is] providing more player agency and clarity about how to obtain them by removing randomness from the process."
Random drops have thus been disabled in-game, and various items have temporarily disappeared until they're ready to return to the cosmetic vendor which will be "reworked in future updates and will be purchasable with Units. This will directly affect random chance cosmetic rewards from completing activities (Missions and Strongboxes) and character progression (Hero Level and Faction Level). Numerous patterns will also be temporarily disabled from dropping and in some cases replaced with additional Units that can be spent at the cosmetic vendor."
The TL;DR version of this is that these changes are exactly what you'd expect from a game that is looking to make a pivot to free-to-play and needs to change-up its reward economy in preparation. That of course is just my speculation and nothing official has been said, but the nature of these things is that the companies involved will deny it right up until it happens. Making the levelling slower, completely re-working an endgame cosmetic system that wasn't doing anything to keep players engaged... you don't need to turn the page to see where this one's going, true believers.
