Whilst there are ways of getting symmetrical speeds over DOCSIS, they would involve a significant upgrade cost and it seems improbable to me that VM would bother with those when they've committed to XGS-PON as their future delivery technology, and that's certain to feature better upstream speeds. If you want to be in on the XGS-PON trials, you may need to move to certain areas of Stoke, Salisbury, or Wakefield, if you don't already live there. Even in those locations it will take time to convert the network, and just because the network is capable of higher upload speeds doesn't mean VM will enable them for customers any time soon.
You might soon see a 2.2 Gbps offer on DOCSIS, with a 100 Mbps upload, as that's already been trialled in multiple locations, I don't get the impression that 100 Mbps cuts it for you?