For clarity, St Albans City already supports contactless, as does many other stations on the north end of the (original) Thameslink, at least as far as Luton (ISTR).
City to Abbey is indeed borderline for an OSI type arrangement, knocking on for a 20 minute walk (1.25 miles, Google maps says 30 but I think that’s generous). But maybe should be allowable in case of disruption on Thameslink.
I wonder if there are plans (or a date) when the capability is extended to Woking (Southwest Main line–last contactless point currently is Surbiton I think) and Chelmsford or maybe Sudbury/ Marks Tey/ Colchester / Ipswich.