A complete real world waste of time and money due to the platforms age and poor condition (from hard war service and limited opportunities to refit and properly maintain them during the war), but at a purely academic level I would love to see some Nelson upgrades and modernisations.
First thing new completely upgraded machinery providing higher speed and increased range as well as increased (AC) power generation. Suppression of X turret in favour of an armoured deckhouse incorporating a CIC and other control features as well as improved accommodation and a number of 4.5" BD DP mounts. Removal of all 6", 4.7", 2pdr and light AA guns in favour of uniform 4.5"BD DP and sextuple 40mm distributed around the superstructure. a comprehensive suite of the latest radars and directors. Space and weight for guided missile when they become available. Aft hanger and catapults for the latest sea / float planes, space and weight for helicopters when they become available.
Phase two would be guided weapons and helicopters the idea being to get either Talos or Terrier and Tartar into service ASAP on these two ships while coming up with a more satisfactory permanent fit for the KGVs and Vanguard.