What is your idea?

Horses and horseraces.

People could own horses, maybe limit to 1 or few (maybe having not enough room in stable). You could sign up these horses to races, which are bet'able from everywhere and everyone. Monday would be race in New York, tuesday in PH, etc. Someone (or game) could own the racetrack.

There would be more than 1 start, so that you could set some tatics, that which start you attend (or depending on horse). Depending on horses stats, game would pickup winner, 2nd and 3rd. They would get price from racetrack owner (announced when signing). If your horse run's today, it would be more exhausted tomorrow, able to run maybe, but slower performance, and next day even more.

Betting would be "easy". You bet only for win, 80% is returned (or similar). if you bet 1$ alone to one horse and whole bet cash was 30$, you get 30*0.8 = 24$. If there was other guy who bet also 1$, you both get 12$, you get the pattern.

If someone wants to give up the horse, it's "destroyed" and new horse is spawned to "auction" (or market). Old owner could not buy new horse until some grace period (maybe). New horse would have new stats. Stats could effect how fast it starts, how fast it can keep up, how long it could run (maybe starts are diff lengths). These all would be invisible to player.

Optionally horseraces could be "aired" in global chat or similar (by game). Track run's would be different times in RL day, so that sometimes anyone could hear airing. Horses could have injuries, maybe steroids, checking antidoping. Or we could start small.

Has your idea already been suggested in some form or another before?

I could not find anything that refers to horses and horsetracks.

What does your idea entail?

Horses, tracks and betting.

How can your idea be successfully implemented into the game as it stands?

Easily, it's totally separate thing. (see below more detail)

What major changes would be needed to make your idea work?

Have all that stuff, buying horses, selling horses, setting races, setting bets.

What is the positive impact of your idea?

It would be fun, it would also create conflicts when you migth get rid of someone just because you want your horse to win. If person dies, horse would obviously be absent (and removed from race). Also if there is that airing thing, it could create real events every now and then people yelling for their bets.

What is the negative impact of your idea?

Possibly horses would be owned by the people who already have the money, but if horse owner would not gain that much money from start and they would only gain money of win (positions 1-3), maybe horses would be more evenly shared.

How may your idea affect the rest of the userbase?

I think it would be fun, and might increase interaction.

Coding complexity?

I know this is bit me quessing, but having one table for horses linked owners, and one table for races (linked to city, row spawned by cron), and one table for starts (linked to races), one table for bets, it's almost there :P Bit of simplification, but almost there, maybe.

You would also need pages like:

horse  handling: buy horse, take care of horse (maybe it needs upkeep), dismiss horse

sign up to race: list of future races, and signup to start

betting for the race: list of races and starts (or just next one), bet for start and horse

Prolly few other pages. Ofc, I don't say it's an easy task, it requires a hard work.

Need coding help on this?

I can help you out, coding it "blind" as separate thing, and you just plug it in (more or less, ofc you would have to do a some work integrating it in). Ofc it would require you to define what kind of DB access to use, and few other parameters, but otherwise main work could be done more or less "blind".