Decades ago when we were still in the House Of Bondage (sic JHN), there was a Church Directory, indicating the level of churchmanship in every English Anglican church which was somewhere on the spectrum between 'Prayer Book Catholic' and 'Full Catholic Privileges'. (And in the episcopopter era, FIF did a list.)
After the hoped-for regularisation of the SSPX, we could (in this on-line age) have a Catholic version; listing all the churches where the EF was celebrated ... or where the OF was so reform-of-the-reform as to be almost undistinguishable ... or where the Ordinariate Use was done in its more 'Tridentine' version ... or where Ukrainian or Melkite liturgy could be had ... you get the idea.
Not 'pure' enough, some of you think? Well, it's how the once-admirable Good Food Guide used to function: full entries for real food but supplementary information about the best-of-the-rest in otherwise arid areas miles from a decent restaurant.
It would be a charitable ecumenical enterprise enabling Tablet readers to know which churches fail to tick their exacting boxes.