Perhaps the solution was to cut the knot....
I seem to recall that GRRM made some comments about the problem concerned timing. And it may well also concern the size
of Essos. Unlike Westeros (south of the Wall, that is), we don't really know how big Essos is. We know that its western shore reaches from directly east of Dorne to directly east of the Fingers, but its extent, east to west, is unknown. We have maps of bits of it, but nothing that links these. Even when Dany was moving about, we didn't get a feel for its true size. And in AGoT, ACoK and ASoS, this didn't matter: we were following Dany and took no particular notice of how her position related to anyone else (and didn't really care much about the time she spent heading this way and that).
But the Meereenese knot involved getting various players into Dany's vicinity in some sort of sequence, and from various start points. That required GRRM to know how far east Meereen is, and how fast various characters can move - over land, down rivers and across the sea - and in a time of conflict. That was GRRM's problem, his "knot". We don't need to know the details of the problem or of his solution, not directly. (And perhaps his solution is something perhaps only he will see in full.) We'll only get to see its consequences, like Quentyn arriving late (appropriately enough) and Marwyn's (apparent) non-appearance in ADWD.
We shouldn't be surprised at this: a lot of what we have seen is a result of Varys's and Littlefinger's pulling of various strings. As has been pointed out, we still don't really know what either of them (or Illyrio or any number of other plotters) is up to.
By the way, Werthead provided a comparison between the size of Westeros and Europe: (http://i36.photobucket.com/albums/e4...arisonsize.jpg
). Based on that map, I reckon Westeros is about 4200km (2600 miles), from the Wall to the southern coast of Dorne.