To be fair, the below are expensive and risky, but we're talking ideal "without fail" here, so...
1: Hire a second team whose sole purpose is to (over the course of several years) re-build the game on a new/modern engine, with extensive documentation, with the end goal of transferring all accounts / characters and guilds smoothly to a more stable and accessible engine (same coders with documentation so that when things need to be changed or fixed, it's easier to do. No more getting lost in spaghetti code ... in theory. Which will hopefully also allow for easier future implementation of other desired features like UI scaling, a proper cosmetics tab, removal of invisible walls and replacing them with actual art assets, fixing of ladder bugs, personal housing with display racks so one can showcase bound loot for others to visit and see but not steal, perhaps even a more advanced graphics toggle where players can choose (personal hardware depending) on Classic style and Gritty (imagine DDO but with Dark Souls or Elden Ring style graphics), re-implement some of the original stealth tactics this game used to boast, like creating distractions by using a ranged attack on a wall to make a sound that nearby enemies would investigate, allowing you to sneak by with a larger range of safety from enemy spot/listen checks, larger/more accommodating bank space, etc).
2: Hire a larger QA team, not just for new content, but to also play the game, quest by quest, to keep all content working and enjoyable. Unlike other MMOs, DDO actually keeps all content relevant via the TR cycle, and thus old content should not be neglected/ignored, and old bugs should not last long as they do now. (it may be a stretch, but include in game customer service into this category, where they are people who also play the game and thus know the game, and can actually help in the moment instead of passing you off to an email system with a dev who may, one day, maybe address the bug, if they can figure it out days later, maybe, if we're lucky)
3: Invest in marketing. The current system of an email sent out to vets with info on new releases to bring them back for a purchase (which indicates the expected cycle is vets stop playing, then they come back for a purchase, then stop playing again until the next release) works for short term / quarterly reports... but is a model that tends to slowly fade until it fails in the long term. For long term profits and dare I say actual growth, new players need to be coming in regularly and constantly. In addition to emails for the on-again-off-again vets, and the short vido clips that are only found on DDO's own websites and social media pages, there should also be adds to get completely new eyes on the product/game. Of course, to retain new players brought in by more extensive advertising, the new-player experience needs to be good/enjoyable and up to date, which leads me to honorable mentions...
Honorable Mention: Revisit the new player experience (not just korthos, but early harbor as well) with a focus on retention via engagement and enjoyment (not via scummy manipulation of human addiction tenancies) so that new players keep playing because they enjoy the game.
Honorable Mention 2: make sure the server hardware is advanced and up to date to be able to handle thousands of players at once per world (including players doing things that in the past have caused server lag) so ensure that it (servers and their calculations of player actions) is no longer a source of lag.
HM 3: encourage regular play time for all the devs and management to ensure everyone is fluent in the game they're a part of making
HM 4: as an extension of the massive rebuild of #1, impress upon the teams that it's about player fun (not manipulating money from addiction), and mandate the slow revisiting of all quests and areas to allow for more exploration and multiple ways to handle situations (allow rogues to unlock more doors instead of requiring kill all X to unlock, make the walkmesh match the art assets, so that if it looks like a character can walk somewhere or stand on a ledge, they actually CAN, and if this means cheese tactics gets introduced, embrace it and adjust the encounters and enemy AI to compensate in a fair/realistic way like melee enemies running for cover or pulling out bows to shoot back at characters on "safe" perch spots, etc)
