In many ways, Super Smash Bros. for 3DS/Wii U was already an “all-star” outing. Sure it wasn’t 100% complete but given that the vast majority of fighting games never reach that bar, it was an acceptable loss. Nintendo ambitiously delivered the series on two platforms at once, added plenty of new content, and even threw amiibo in the mix, which became a smash hit of its own. It was a triumph.
Of course director Masahiro Sakurai would try to outdo himself with Ultimate.
Source: Destructoid Review: Super Smash Bros. Ultimate