I believe the completed crossword should look something like this:

>! [![Completed crossword, using all English letters][image1]][image1]

Or, alternatively, in the spirit of this month's [Topic Challenge](https://puzzling.meta.stackexchange.com/questions/7406/monthly-topic-challenge-4-cross-non-words):

>! [![Completed crossword, using Japanese characters in place of some two-letter units][image2]][image2]

What's happened here? Well, it turns out that in order to fit all of the words into their spaces, we have to...

>! ...replace some two-letter units with their equivalent **Japanese characters**. Here I have chosen to use [hiragana](https://www.unicode.org/charts/PDF/U3040.pdf) rather than katakana (if this is the wrong thing to do culturally speaking, I plead ignorance - I knew next to nothing about Asian alphabets before ending up deep into solving this puzzle...).  
>!  
>! Note that in some instances (marked in red characters in the first diagram) the same symbol (or a variation on the same symbol) can be used to represent multiple different two-character units, e.g. the TI and DI in the very first box. In these instances I have chosen to portray the simpler of the two variations in the diagram.

As for the landmark represented in the crossword, I believe this is likely to be:

>! **Tōkyō Sukaitsurī** (a.k.a. 'Tokyo Skytree') - a *neo-futurist* building (hence the title) in the Japanese capital:  
>!  
>! [![Tokyo Skytree][image3]][image3]  
>!  
>! This does end in the 'RI' present in the grid in answer 2A. However, I must confess I am at somewhat of a loss as to what the numbers are intended to represent here, or why there are four grey boxes in the crossword grid indicating the vowels U, O, A, and E...

A full list of my clue answers is available here, with available grid space enumerated in square brackets:

>! **Across:**  
>! 2. Dormant Javanese volcano and abandoned nuclear power plant site (5) **MURIA** [3]  
>! 4. Walking with _________, first in a series of documentaries (9) **DINOSAURS** [6]  
>! 7. Mercury crater named after a 19th-century American novelist (9) **HAWTHORNE** [6]  
>! 10. Barry _________, loser of the 1964 US presidential election (9) **GOLDWATER** [7]  
>! 12. Indian alternative medicine system (8) **AYURVEDA** [6]  
>! 14. Soap opera that debuted on the same day as Channel 4 (9) **BROOKSIDE** [6]  
>! 16. Direct current generators using commutators (7) **DYNAMOS** [5]  
>! 18. ______ Hill, female Australian composer (6) **MIRRIE** [5]  
>! 20. White Star Line ship, later Gülcemal (8) **GERMANIC** [5]  
>! 22. "The better wow", per Urban Dictionary (5) **WOWIE** [3]  
>! 23. Small, often domesticated lizard (6) **IGUANA** [5]  
>! 24. Follower of Network or British (4) **RAIL** [3]  
>! 25. Squirrel's nest (4) **DREY** [3]  
>! 26. Nose pimple caused by excessive drinking (3-7) **RUM-BLOSSOM** [9]  
>! 27. Constellation containing the Spare Tyre Nebula (4) **GRUS** [3]  
>!  
>! **Down:**  
>! 2. Pondered deeply (5) **MUSED** [3]  
>! 3. Touch by means of a mutual border (4) **ABUT** [3]  
>! 4. Yes album before The Yes Album (4,3,1,4) **TIME AND A WORD** [9]  
>! 5. Wood-cutter after the tree has been chopped down (5) **SAWER** [3]  
>! 6. Enyaq manufacturer (5) **SKODA** [3]  
>! 7. Pointed end of a hook, or a fish caught by it (4) **BARB** [3]  
>! 8. Anatomical homologue of the human ankle in a horse (4) **HOCK** [3]  
>! 9. Genus of duckbill eels (12) **NETTENCHELYS** [9]  
>! 11. Escher lithograph featuring a compound of three cubes (9) **WATERFALL** [8]  
>! 13. Saint Paul's role as author of Galatians, Romans and others (8) **EPISTLER** [7]  
>! 15. Component of an internal combustion engine pushing the intake/exhaust valve (6,3) **ROCKER ARM** [7]  
>! 17. viz. (6) **NAMELY** [5]  
>! 18. _______ Aouragh, Dutch anthropologist (7) **MIRIYAM** [5]  
>! 19. Genus of the black-winged kite (6) **ELANUS** [5]  
>! 21. South Korean League of Legends player currently playing for Rogue (7) **MALRANG** [5]

  [image1]: https://i.sstatic.net/f7tyH.png
  [image2]: https://i.sstatic.net/XY4Ai.png
  [image3]: https://i.sstatic.net/GbYVZ.png