I think that BA are not making ANY changes to the fares except eliminating the standard (V1 fare basis). Right now we have four fares (HBO Z0, Standard V1, Semi-Flex V2, Fully-Flex V3). The document says that from March 8th there will be three (HBO Z0, Semi-Flex V2, Fully-Flex V3). I think it is wishful thinking that any fare pricing will change for Semi-Flex - it is clear that all is happening here is removing the Standard choice offering.
Moreover the features advertised for the new Semi-Flex are the same as for the current Semi-Flex - no changes whatsoever.