I find it quite impossible in practice, to "split the miners into 2 equal groups by causing a communications delay between them".
It's probably even harder than splitting the internet in half.
If you look at this hashrate chart, you can see that by just targeting the 4 largest pools you could split the hashrate into 2 equal groups. So much easier than splitting internet in half. Now still there is the requirement of isolating a merchant node, so that it is only seeing blocks from one side. But problem seems halfway solved with 4 pool attack.
http://i.imgur.com/iebKjrg.png