The issue comes with the idea of Warp 10 being equal to infinite velocity, in which an infinitely fast ship would travel infinitely fast, occupying every point in the universe simultaneously in the process.Transwarp was dumb, but Changelings altering their mass along with their size and even flying at warp speed is at least as bad.
there is some... just plain... stupid stuff in startrek. warp10/transwarp it should ALL be the same. instant travel thats it. plain and simple. not everywhere at once, just... instant.
Under those conditions, Warp 10 is merely an abtract concept, a term used more to cap the warp scale than anything else, because it's otherwise an impossibility.
But with transwarp--which is probably any velocity in the Warp 9.999+ range--a ship could move at really "stupid fast" velocities without ever reaching infinite speed. Beings like Q could appear to move instantaneously across the Universe, while still not being quite at Warp 10, IMO.
But it does become cumbersome and silly after awhile. Warp 9.99999675, for example.the warp scale is awesome... just keep adding 9's after warp 9.9 to go faster. simple, easy.
The term "transwarp" could be a shorthand for any Warp 9.99+ velocity on the new scale. They can simply say "transwarp" for short and avoid having to say something like Warp 9.9990...if the federation cannot make a ship obtain a warp factor for 9.9990 ....the how could they ever reach transwarp?