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By this time next year, I'll have visited most of Japan's famous places.
Literal
Next-year [possessive-の] this-time-around [by-までには] Japan [possessive-の] famous places [object-を] almost visited [ことになるだろう] (will-be-the-case-probably).
~ことになる ('it turns out / will be the case') paired with だろう conveys future uncertainty — 'it will probably turn out that [I have visited]...' 訪れた ('visited,' past) inside the の-clause marks an accomplished state. までには ('by the time of') is the future deadline marker, with は adding topical/contrastive emphasis. A complex temporal hypothetical.