In the immediate future, there's absolutely nothing wrong with getting us back to 6th. It would mean we're back in Europe, with hopefully a stronger, more expensive and more valuable squad, with a possible ground move on the horizon. That would be an extremely strong position.
I'd love us to jump into the Top 4 next season, but even with Emery that would be very difficult. So I have no issue with Koeman hopefully getting us back to 5th/6th next season, and maybe a cup win. It's unlikely to be a longterm appointment either way, so if Koeman's able to achieve what he did at Southampton with us in 2/3 years, we'd then be in a much stronger position to go for an elite manager, and have a long term, sustained chance at Top 4.