Leaked excerpts of Masahiro Sakurai's weekly Famistu column have apparently revealed that during development of Smash Bros. Ultimate, the series creator and the team considered using a popular coding solution used in other fighting games to improve the online experience.
According to PushDustin on Twitter, the column will discuss changes to the game's 1v1 online mode. It reportedly suggests that rollback netcode was investigated while the character-based brawler was in development, but it had unintended side effects that the team obviously didn't feel it could overcome.
These 'adverse side effects' haven't been detailed yet, although with multiple players online, plus intricate stages, items and other factors, it's not difficult to imagine issues cropping up.
For anyone not up on their netcode lingo, rollback netcode (as opposed to delay-based netcode) is often favoured by fighting game fans for a more satisfying, snappier online experience. In a nutshell, delay-based netcode delays updating the game state until player inputs have been received from wherever around the world they've been sent, and is therefore very susceptible to network fluctuations and often results in a chugging experience for both players - far from ideal in a fighting game.
Conversely, rollback netcode does things differently; it logs when inputs are received and adjusts (or 'rolls back') each player's simultaneous game state to match. This can result in players appearing to 'teleport' as new input info is received, and can also lead to desyncing between each player's games, but generally offers a smoother online experience.
For a more thorough explanation of differences between delay-based and rollback netcode, we recommend reading through Ricky "Infil" Pusch's article on the topic. Neither solution is perfect, but consensus in the fighting game community tends to favour rollback netcode. In fact, earlier in the summer a fan-made update to Super Smash Bros. Melee added exactly this type of netcode to the GameCube entry, and it seems to have gone down very well with the homebrew Smash community.
It'll certainly be interesting to read Sakurai-san's perspective on 1v1 online Smash, as many fans aren't satisfied with the Switch entry's online component. We'll update this post with more information when the full article is released.