The problem with providing dates is that it has all been done before with the various previous cable companies we have had. Well, they often used to say 'before the end of the year' or 'by summer' etc. for upgrades. As we all know, these were either wildly inaccurate schedules (often out by 3 or 4 years) or simply pipe dreams (still waiting for CLID on the phone even now).
Basically, if you look at the history of upgrades for your exchange, and you remember this is the largest amount of work needed for an upgrade yet (as mentioned in an earlier post) you can work out a rough idea of what will happen by adding a little more time to the scales you have experienced before.
So, in Southampton, historically, the likely chain of events will be that it will take about 3 years of fannying around before the cable company admit it is 'not cost effective for your exchange and won't now be rolled out in your area' and we settle in to wait for the promises of the next cable company to come along.
Still, sometimes we get there, so the optomistic timescale based on past Southampton success stories would be about 3 years plus a bit for the big job this is, so between 3 and 4 years. Given VM's stated confidence I am really hoping we get this kind of time scale, so I'll be cheering you on through the hard slog of beating our exchange till it submits!