I spoke to Vodafone today about WKH and for the first time got what seems like a logical explanation for what is going on in Island Bay. This is a third-hand layman's explanation, so I apologise if it's not entirely accurate, but the gist should be correct.

When Vodafone upgrade a node they cut half the node over at a time, then spend time analysing, tweaking and re-balancing the connections, presumably only impacting those users on that half of the node. WKH is different in that it has six or seven other nodes hanging off it, making it impossible to approach in the same way, as any changes would have significant flow-on effects. Instead, they are making smaller, progressive changes to those "child" nodes to eventually remove the dependency on WKH, once that's done they will be able to cut WKH over. While there might be some improvements to WKH by removing those dependencies, my understanding is it will not fix WKH.

While I couldn't get any indication of timelines, it seemed clear that this was a long and delicate process and a fix cannot be expected any time soon. Any suggestions here that WKH issues could be resolved in the next couple of weeks are nonsense and any claims of a potential fix this week are simply wrong. 

Vodafone have offered to work at tweaking my individual connection in the hope of some improvement and have asked for speed tests and traceroutes over the next few days. I'm going to work with them to see if I can get something acceptable, while I'm testing alternative connections. ADSL2 will go in on Tuesday, hopefully it won't be a long wait for the VDSL upgrade.

TLDR; WKH will not be fixed any time soon. There may be some hope in dealing with support to fix your individual connection, but no guarantees.