I know you are EU, so technically it may have come in 'late' but if you've been playing this last year, you know we've had a bonus almost every week and a few were communicated late(this one here...for US at least...was several hours before reset). A good rule of thumb is if you don't know for sure what the bonus is, hold off on anything you cannot sit on cashing out. For legion that meant 1 raid and 1 alert. You could have done the outdoor missions and held off on cashing in till after reset. There is almost always a bonus week before a new episode, usually on either A) the outgoing currency (BOP here) or B) the current currency. Hedge your bets and hold off till after reboot if you are that concerned about it. That having been said, once the decision is made, it would be nice to have a in game message pop up at login (Next week's bonus Legion 3x, after tonight's server reboots). Now some people would even have an issue with that as maybe they logged in before that message and wouldn't get it...or they don't have the chat tab showing system messages...or whatever. While I agree that 24 hours notice would be better, it's at least in part on us to check before assuming. I know I didn't have any idea what the bonus was as reset approached, so I went to the site and checked..."Hey....3x marks...goodie" was I believe what I said.
