Can't see it happening personally, irrespective of the Koeman situation. He would however, solve our problem of struggling against the lower side who make incessant crosses into the box, long balls and rely heavily on set pieces, due to him being
insurmountable in the air. On that note, not only would he useful in terms of defending set pieces, but also attacking set pieces given he scored 3 goals this season. He's predominantly utilized on the left of central defence meaning Smalling would be able to carry on playing on the right, where he feels more comfortable, and this is imperative given his apparent limitation on the ball. He (Smalling) does have the ability as we saw at times in the 2014/15 season, but he seems to have slightly regressed in that regard, in the subsequent season. I'm of the opinion that Van Dijk has been consistent, and quite deserving of being both Southampton's fans player of the year, as well as players player of the year, but he is susceptible at times to being bamboozled by strikers with the perhaps the most notable examples being
and
http://i.imgur.com/ghpeT30.gif
All in all, he'd be a significant improvement, but I just think it's unlikely. I do remember feeling disconcerted when Van Gaal didn't show any interest, whilst the club fallaciously believed Ramos actually wanted to come. Van Dijk is one of the best central defenders in the EPL imo.