While i cannot verify the authenticity of it, it appears blizzard will attempt to pioneer a technology that will make your PC the server instead of the always online D3 currently uses. I shall C/P a few bits from it but read it yourself.
"In a surprise move today, Blizzard Entertainment announced that their hotly anticipated forthcoming game Diablo 4 will feature a new technology they’re calling LocalServer™. Blizzard claims that the innovative feature will allow players to run the single-player game entirely on their own computer. LocalServer™ promises to all but eliminate contact with the battle.net servers for standalone campaigns. Critics say that this level of cloud-independence is technically impossible, but representatives at Blizzard seem confident that this daring innovation will work.
Incredible as the advance may sound, Blizzard claims that after years of intensive research they are close to perfecting the feature. “Back in 2012, when we originally released Diablo 3,” recalls Lead Programmer Baken Sizzlen, “it was assumed that any game must necessarily involve both a local client and a remote server. It simply seemed infeasible to provide game server software that would run on client computers. Handling complex computing tasks like processing mouse clicks, moving objects along straight lines, and allocating memory to store newly-spawned zombies are just too expensive for a client PC. Battle.net simply had to lend a hand.”"