I know there are a lot of people that are absolutely opposed to any changes made to the game other than tweaking and balancing but hear me out.
What if Blizzard implements regularly updated multiplayer melee gameplay like other games, say one ladder season per meta (except obvious balance changes).
At this time, the Warcraft 3 player base is pretty small in comparison to a lot of other titles out there (hopefully Reforged brings a lot of people back and new players to try it out) and a game that gets regular meta changes would make it more exciting thus bringing in more people.
My suggestions are as follows:
- New items added to the game regularly for mob drops;
- Old items updated to balance it out;
- New mechanics (like what they did in the latest patches) but updated/added/removed regularly not once every 10.000 years;
- Add new modes to play ladder, like full random (random race + random race hero/tavern hero);
- A bit of slowed down gameplay, especially for 4v4, like putting in requirements (not just altar, lol) for T2 and T3 so that people don’t rush it every other game;
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- Add a point system or ladder XP increase based on other metrics such as healing done, damage dealt, debuffs/buffs applied etc. - on the same note, make the game keep track of more stats for melee players’ profiles like average APM, avg. number of units they produce, avg. number of buildings, avg. number of kills, you get the gist.
- Maybe, just maybe, new heroes to the tavern until its filled out? (not a must but just throwing it out there);
- Standardizing drop-table rules for melee maps to make farming harder creeps more worth it (for example, lvl 1-2 creeps drop tomes, 2-4 drop a usable item, 4-6 drop a permanent item, 6-10 drop powerful permanent items + tome of power or something on those lines) - Its pretty crappy when you fight a hard creep camp only to get a scroll of the beast that you might sell or you may keep it just in case but it rarely makes a difference in a fight - feel free to correct me on that one because I sell it every time;
- New item effects - Since Orb of Slow offers the possibility to do a lot of things with items almost on the level of WoW on hit chance effects, why not - just don’t make them OP and boom;
These are just a few suggestions, to keep the game up and running for another 10 years.
But last and not least, keep track of what units/heroes are not used because they are bad (oh boy some are bad) and update them accordingly.
*if adding a point system to reward better players with something, you can add visual queues only (nothing else) like a border around their name when loading melee AND/OR name/level color change to WoW item rarity colors (1-9 white, 10-19 green, 20-29 blue, 30-39 purple) AND/OR titles but nothing that impacts gameplay 
(contrary to popular belief, these things really appeal to some people)
If you got so far, you may be wondering whats the difference between this thread and other suggestion threads and whats its purpose: difference is that this suggests a change in mindset for the future of WC3 and its purpose is to throw in some suggestions that repopulate the game servers so that melee competitive play becomes better than its current state - it would also revitalize the moding community and who knows what new type of game comes out of it (especially with 12v12 gameplay now available which is very hard to get a full lobby in a timely manner).