I would only loan him if it was the difference between us getting him or City/United. He would be much better off marking Lacazette and Aubameyang in training and getting a taste of the Premier League, even if he's not up to regular football. From what I've seen and read about him, I think he's more ready than most realise.
I'm hoping the stories emerging about the kid agreeing personal terms with Arsenal, is actually a case of Saint Etienne accepting they were going to have to sell and allowing the kid to talk to all the interested parties. If we have beat out City, United and whoever else, then that's a good sign. And if it has gone down like that, it should mean a agreeing a fee will be a formality because there must have been a basic agreement between the interested parties and Saint Etienne prior to them allowing clubs to present their case to Saliba. If they were adamant they wanted a loan they would have said so from the off.