Complete conjecture, but is it possible that having taken Trebizond in 1461, Mehmed II's intention was to next launch an invasion of Italy? A thread on why that might have been the case...
In 1460, Florentine merchant-spy Benedetto Dei recounts that he gave an interview to the Grand Turk who wished to know details of the political situation in Italy. Dei appears to have concluded that Mehmed intended to launch an invasion & claims he tried to dissuade him.
He told Dei: "Mr Florentine, I have heard all you have said...& I believe it fully...but I answer you & say that Italy could no longer perform the great deeds it performed in the past...today you are in disagreement among yourselves"
He was right. A bitter war over the crown of Naples had southern Italy in disarray. That year (1460) one of the protagonists, Ferdinand, hired the great Turkish nemesis Skanderbeg to cross from Albania & fight for him. Meanwhile southern Greece (the Morea) fell to Mehmed. 
The next year (1461), while Mehmed was finishing off his conquests along the Black Sea coast, an artist called Matteo de Pasti was stopped by Venetian forces at Crete. He had been sent by the Italian mercenary Sigismond Malatesta to be Mehmed's court painter.
Among his possessions, the Venetians found a detailed map of the Adriatic coast - an unusual item for a portrait artists to be taking to Constantinople. De Pasti was re-routed to Venice for questioning & the map never reached the Porte.
Is it possible that the invasion, which landed at Otranto in 1479, was originally considered for as early as 1462. If so what might have delayed it? How about a disaster on the Danube in the winter of 1461?
Medieval Wallachia was a hinterland kingdom sandwiched between Hungary & the Ottoman domains which flipped its allegiance between these two, depending on who happened to be holding power that year. They got through voivodes pretty regularly.
The ruler in 1462 was no friend of the Hungarians. Vlad the Impaler had already fought off 1 Hungarian-backed coup in 1460 but he was also no friend of the Turks & had stopped paying the jizya tax. In late 1461 the Porte, probably as an afterthought, decided to remove him.
The plan was to lure him to the Danube fortress of Giurgiu, there to meet & escort a diplomat (Thomas Katabolenos) to his capital. Hamza the bey of Nicopolis was then lying in ambush to arrest or kill Vlad at the meeting point.
The ambush was botched. Vlad killed Hamza, Katabolenos & his men (impaling Hamza highest in deference to his rank). Then as revenge, Vlad burned every settlement along the southern bank of the Danube, killing thousands in a devastating winter raid.
That wasn't something to be left unanswered. Whatever Mehmed had planned for the 1462 campaign season, it was now going to be invasion & decimation of Wallachia & Vlad. The results of this were mixed. Vlad was removed but not killed (he fell into Hungarian hands instead).
By the following spring, the political world hand changed. The Neopolitan wars were dampening down. The Pope (who had called for a crusade in 1460 & received no backing) now had Venice & Hungary signed up. Bosnia was in crisis & potentially easier meat than Italy.
The Long War with Venice (1463-1479) then took hold. As soon as it was concluded, Mehmed launched his invasion of Italy at Otranto but died (suspiciously) before it could gain a proper footing.
That doomed invasion of Otranto faced a Ferdinand of Naples who had been securely on his throne for 2 decades & was no longer at war with his neighbours. It was a much taller task than it might have been in 1462. Friday fun, but who knows if Italy was once saved by Dracula.
