It feels like the U23 thing is for the benefit of the tribunal panel as much as anything. The fee we have to pay is for Chelsea's development work, by publicly saying he's not ready for the first team yet and he'll be with the U23 squad it gives the club ammunition to undermine Chelsea at the tribunal and chip away at the fee. A fee of £3m was probably reported in all the papers for the same reason, that's Liverpool's opening negotiating position.
Obviously what Solanke has been told in private about his squad role may well differ, it's hardly unheard of for young players to progress quickly sometimes...