As I recall very few pianists could tackle its demands until Ogden revived it in that historic recording from 1967.
It is frequently asserted that the "extreme" length of this concerto contributed to its lack of popularity in the decades following its premiere. [The suggestion being that it was too long for audiences to sit through, rather than being over-taxing for the soloist - making it more of a 'programming' issue, rather than a 'performability' question.]
Yet is this really the case? Both of the Brahms PCs - surely the most popular prototype for a 'high romantic' piano concerto - run to 53-55 minutes, depending on who is on the piano stool. The margin of difference between this and the Busoni concerto is almost insignificant, surely?
As for the "demands" of the Busoni concerto, most of negative criticism of the work in its early years was exactly - that the orchestra has the lion's share of the motivic material, and the pianist is slogging away in the background for much of the time? This is not to talk the piece down at all - it's a 'concerto' in a more baroque sense, like a 'concerto grosso', than the flashy showmanship of the composer-pianist-soloist genre of piano concerto (of which Rach 2 is a good example, from the same period as Busoni's)