Why 225088 Gonggong is not a dwarf Planet yet? Per definition a dwarf planet is:


  a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape1, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.


The Wikipedia page for 225088 Gonggong, former 2007 OR10 states three possibilities for its dimensions:


  
  1535+75−225 km
  1280+210−210 km
  1200+300−200 km
  


Which is all minimum 1000km in diameter. So how can you still doubt the hydrostatic equilibrium for such a large body?
As the comments already say, an object being a dwarf planet is a matter of convention. If the IAU says it's a dwarf planet, it's a dwarf planet. Otherwise, it's not. The requirements you are listing from Wikipedia are the IAU criteria for pronouncing objects as dwarf planets, but that does not mean that all objects fulfilling these criteria are dwarf planets. (don't ask me for the reasonings of the IAU, i'm not an expert on astronomer's brain twists)

There are a lot more examples of objects that could be dwarf planets, and are considered as being that by many researchers, despite these objects not having the status of dwarf planet. Wikipedia's List of possible dwarf planets has about 200 objects facing the same issue as 2007 OR10.

edit: as someone in the comments mentioned, not all objects on this list are actual candidates for dwarf planets (which is not what I meant, but I might indeed have implied this)