A friend has just asked me which European sites are still missing from the list. I tried to think and came up with a surprisingly long list of about 40 (!) sites. So my conclusion - yes, there are still important European sites missing!
UK: Oxford/Cambridge as early university towns (not even on the T-list due to their the universities' objection since there are already many tourists), some major railway sites from the time of the industrial revolution (e.g. Forth Bridge), Jordell Bank (history of science), Mackintosh in Glasgow (planned for T-list), St Andrews (golf history, planned for T-list), Newmarket (horse racing, planned for T-list), Brighton (history of mass (working class) beach tourism)
Greece: Knossos (Crete - major Minoan site), Santorini (planned for the T-list for both natural setting, folk architecture and the archaeological site of Akrotiri)
Germany: Nuremberg (Nazi sites), Bayreuth (Opera House), Hamburg (Speicherstadt), Saechsische Schweiz (planned for T-list)
Czech Rep.: Spa Triangle (Karlsbad, Mariabad, Franzensbad), Sites of Great Moravia
Belgium: Westhoek (only major site from WWI)
Cyrpus: Famagusta (now in Northern Cyprus so not on T-list)
France: Hangar Y (history of aviation), Camargue (natural), Carnac (megalithic monuments), Cote d'Azur (mixed natural and cultural, only natural on the T-list), Le Corbusier
Ireland: Clonmancoise (Celtic Christianity still unrepresented)
Italy: Capella degli Scrovegni (Giotto), Certosa di Pavia (the most significant in Italy), Lago Maggiore with Isola Bella, Via Appia, Carrara marble basin
Portugal: Coimbra (university)
Russia: Kremlins, Bolgar Ensemble, Ural NP, some Communist architecture in Moscow or Volgagrad (not on T-list for unknown reasons) and many natural Asian sites (e.g. Lena Pillars)
Netherlands: Keukenhof (flower growing, not on T-list probably because there already many tourists)
Denmark: Tivoli (amusement park, not on T-list, probably the same reason)
Urkaine: Krim, Chernobyl!