Long time since an update, but thought I'd post some additional information.
A while ago I was in contact with a member of the Liberty Global network team (can't reveal specific details at their request), who had seen the posts around the IPv6 tunnels issues and wanted more information (the power of LinkedIn!). By now most are aware what has been discovered is despite all previous doubts and finger pointing the 6in4 speed issue is a hardware one, not artificially created by Virgin Media i.e. deliberately slowing the traffic/routing etc. From their tests, they could not find any issues with the speed of 6in4 within their network only when behind a CPE, so the CPE was being pointed at as per the comments from their spokesperson in the ISPReview articles. This has in fact now been found to be the issue, more and more people have been able to confirm that the Hub4 does not have the same issues with 6in4, because of it's hardware being faster but this is probably by chance than specifically fixing this problem. The CPU processing power in the older modems is the bottleneck it would seem. The articles from ISPReview hint at a firmware update, I'm honestly sceptical about anything happening here. The lead time for firmware updates is long, it affects all previous modems other than the Hub4 so multiple vendors and ultimately 6in4 is niche. At this point the logical option would be to simply acknowledge the 6in4 speed issues (which they have done publicly) and just put all resources on a native IPv6 rollout, resolving two problems, the 6in4 issue becomes redundant.
Most will also be aware the Hub4 is only available to those who are in DOCSIS 3.1 area, this has been steadily increasing over last few months and will continue into 2021. In the beginning Virgin Media would not let you get the Hub4 without being on the Gig1 package, this however is no longer true, despite some of their support staff telling you otherwise. Virgin Media have been offering the Hub4 as a free upgrade to some, although the motivation for this, is simply to help the DOCSIS 3.0 network with congestion. I don't believe you can just request the Hub4 even if your area is DOCSIS 3.1 enabled (unless you take the Gig1 package which the Hub4 is mandatory by default). Virgin Media still seem at this time to be approaching customers directly for this. Despite not being in a DOCSIS 3.1 area, at one point I was going to be offered the Hub4 to test the theory through some internal channels. While the Hub4 can technically work on DOCSIS 3.0, ultimately I decided to not take this, because I would be basically waiving all standard support channels if anything went wrong given it is not a standard deployment and given work from home, this seemed too risky for something like 6in4. I have since moved on from 6in4 and instead use the L2TP service from AAISP. I also have another WAN now (Vodafone FTTC) which I can point a 6in4 tunnel on and get full speed, given it isn't behind a Virgin Media CPE, but ultimately 6in4 shouldn't be the permanent solution either anyway.
Regarding an IPv6 deployment from Virgin Media, there was very little information about this from the contact I spoke to. I sense the concern is they don't want to state anything because they can't officially speak on behalf of Virgin Media, they were however OK with mentioning the Hub4 as a "solution", although it isn't really, a native IPv6 deployment is. I got the impression that the 6in4 scenario getting some traction did start some internal discussions within VM on IPv6 and perhaps conversation were had, but nothing seems to have materialised since. Virgin Media Ireland is still going strong with DS-Lite IPv6, I've seen various posts from VM Ireland customers confused as to why port forwarding and modem mode options aren't present, until you explain that VM Ireland deploy DS-Lite by default and you have to request to be switched back to IPv4 only for those options to be enabled in the firmware. Many seem to think DS-Lite is dead for Virgin Media in the UK, given the IPv6 trials were mid 2018 and absolutely nothing public has happened since, suggesting they may have decided to abandon it. They weren't exactly in a rush to deploy IPv6 anyway but it possible they've decided it's not a good idea. The evidence of DS-Lite was strong, given parent company Liberty Global absolutely loves it and it's deployed in a lots of a other countries where they are but rumour says they might not. That however is entirely opinion and there's no official comment on DS-Lite being abandoned.
