Biaggi is never going to race the Ducati competitively and are some really thinking he is going to spook Rossi if he turned out on it. The only time they'd meet on track is on the formation lap and when Rossi lapped him.
Back in the early 2000s they were a close match, especially on the 500 bikes but Biaggi threw his down the track a few times too often whilst leading Rossi and with it any chance of landing the title. The 500 era was his best chance and he missed it. On the 990s the early M1 was not on a par with the Honda V5, carburettors and not even 990cc (maybe not even 900cc from some reports) left Biaggi with not much hope against Rossi and the mighty 990cc V5. When Biaggi got the V5 in 2003 he still couldn't beat Rossi and trailed Gibernau too in the final standings. When he finally got the Repsol Honda in2005 he had one of his worst seasons ever and his Motogp career was finished.
His results in WSB lacked any consistency and it took until he got the Aprilia to challenge for the title.
So what is it that some see as him being able to rattle Rossi if he turned out on the Ducati? Rossi's the one with the titles, not Biaggi, Rossi isn't the one who ended up the loser of the two in any personal rivalry that existed. No doubt they can both wind each other up as they genuinely seemed to hate each other, but on track, now, in Motogp, Biaggi would come off sorely worst.
Why do some think he would be good for Motogp. Saying he would be a sponsors dream and / or attract more viewers is surely being more than a little hypocritcal after criticising Yamaha for signing Rossi for his marketing potential rather than any belief from the race team that he can win again. I don't get the devlopment angle either. He isn't going to ride that bike as fast as Dovi or Hayden, therefore it's questionable how valid any feedback he gave would be. This is the man who was a complete twat to work with and would never accept any blame for bad results, it was always someone else's fault. At constant loggerheads with crew, team and other riders. The man who was given a Repsol Honda and supposedly called it junk whilst throwing it on the floor in the pit garage. Imagine what he'd do with the Ducati - assuming he'd make it back to the pits with it in one piece....
The man Lyn Jarvis decribed as being far worse to manage for one year on his own than Rossi / Lorenzo in their first stint together at Yamaha. Does any team want or need that?
A stand in for Spies? No, he's not fast enough, just Biaggi indulging himself at the Ducati test as they had a bike going spare. Interesting for some but nothing in it. There is no specific timescale for Spies recovery, could be sooner, could be later but there has been no mention of him sitting out the rest of the season.
He'll be back