I doubt this is likely to be implemented.
The structure of the game revolves around the fact that one person is hosting. It is that person's farm and everyone else is really just an extra. You can't just take over someone else's property/business without that person cooperating... which is easily done by them sending you the save file and you loading it up. Or you could both load up the mod that allows the host to be switched and do so. Either way, you can't steal the farm.
If you can't get that person to send you the file, I'm sorry, but you'll have to start a new one. And hell, that could be an opportunity to apply what you've learned to make an even better farm this time.