I don't think koeman would mention it/answer the question unless something is, at the very least, being worked on. By that I mean we are sat around a table not quite down to the finer points but far enough along we are confident a deal of some sort can be done.
On the face of it Everton signing Diego costa is a no brainer but I think his heart is set on atletico so it would definitely be a loan. If it's a season long loan I'm in. If it's till January I'd be questioning the point. The lads been fucking about in Brazil for nearly 4 months. It's going to take a monumental effort from him to be reasonably match fit at any point before the end of September. So for realistically 3 months of the season is he worth it. If he knows he's getting to atletico in January is he going to put the effort in, will his character upset the squad balance?
So if it's till Jan I'm not keen, if it's the season it would be worth it.