I am trying to avoid saying it but these eci cabs were a very poor decision. They should be replaced.
With respect (and remember I'm on an ECI cab knowing that I would fare much better on a Huawei cab & getting higher speeds), I really don't know where the blame lies on this.
1) BT has always gone for diversity. For a company of their size it makes business sense not to rely on one manufacturer. Going right back to the days when ADSL very first started they used different manufacturers. Ive been around long enough to know that at one time the Juniper DSLAMs were better than many of the others and less problematic when 2Mbps adsl was introduced.
Moving on to maxdsl and adsl2+, all of a sudden there were issues with the Marconi MSANs in that they couldn't cope with the higher upstream speeds- yet previously the Marconi MSANs were cutting edge for rate adaptive dsl. Go back in time and they also had system X and system Y for telephony.
2) Ironically ECI was cutting edge when it came to VDSL. In 2012 they were considered the better VDSL dslams. iirc ECI made a lot of progress in vectoring dslams. Problem being they weren't on the M41's.
Huawei late had the edge in that they were bigger units and therefore the backplanes could be upgraded to install a vectoring unit. ECI had gone for try make the cabs as small as possible for the M41's which as the time was a good thing as they could hold more users floorspace wise.. which was also good when you had several districts complaining how ugly VDSL cabs were.
3) BT were not the only telco caught up in the ECI problem, Duetche Telekom was another, but there were more. iirc Duetche Telecom had to upgade many of their cabs to V41s.
Finally Im not chuffed that Im on an ECI, so I really have no reason to defend them just trying to explain some of the history and that 5+yrs ago then ordering ECI wasn't so stupid as what it seems without the benefit of hindsight. I'm really struggling this week, I still have to do a LOT of admin behind the scenes that no-one sees so I'm just typing whilst I can which is very slow. I'm sure ejs will correct anything I remember incorrectly and can add links if need be as Ive just blurbed.