The last turn based rpg i played was FF9. It wasn't bad experience, exept the 2nd player would only be able to play when a battle occurs, while 1st player would do everything. I think the latest Tales of games or their recent HD port had like 4 player coop.

I wish their were more local multiplayer arpg like secret of mana.

While Tales isn't turn-based, I must admit I've had tons of fun doing battles with three other buddies at my side. Sure, they can only play when in combat, but still, it is an amazing thing when you're facing a fierce boss and have to coordinate with everyone! :P

Think about the people who usually play these games.

This.

It could be done and it would work, but would offer very little in most cases so is a waste of resources. If you really want you can just trade the control between you and whoever you wanted to play with lol (I presume you mean co-op versus competetive) 

Edit: Maybe not a waste of resources for an offline game.

Never played FF9? You can play that game with up to 4 players.

You can change which controller controls what character. Tons of fun, I tell ya!

Then I can't see how a turn based rpg would work out online. Unless you're not playing for the story but only focused on playing against other people. Sorry, but these 2 things are not compatible imo.

Valkyrie Profile Profile 2
FF9
FF4
Digimon World 2

Have multiplayer

generally, these games just tell the story from one side of the battlefield, facing nameless mooks and monsters with just the leaders being a bit more special. In other words, there's just not much to play on the other side.

Also, very few people actually play these multiplayers if they have any, simply due to preferences of players who like turn based games in general but also because they tend to drag on as one small error can tip the scales on the whole battlefield