Tbh I think Lip can NEVER be an assist trophy in Smash, if Sakurai wanted to make her an assist he would've done it by now. (we know his affection for the series, which inspired him to work on Meteos.) Instead he wants to represent her as an item which is more complicated for debate, as some items are used in other fighter's moveset. The references are too obvious for him not to know about and they were put in intentionally, heck we know the assets can already be created to be an assist such as using the Garbage Blocks and Mii outfit to build the character Lip but ultimately pointless because of a Thwomp assist trophy. (Another Kirby Stone Transformation) Its also too much stage control with how large the Garbage Blocks would have to be. Maybe Saki and Famicom Wars soldiers were removed because the assist was too similar to an existing one and it seems to not interact that much with the fighters when summoned. (Spawn soldiers, shoot only projectiles horizontally tbh not much of an interesting assist trophy. Fighters move around the stage all of the time. The assist also looks very effortless to make.)
Suddenly Panel de Pon gets more representation than Advance Wars and Sin & Punishment despite the original content being represented from a Japan-only game.
The topic of debate for Lip has always been weather or not she will be in the game. Her being very unlikely to take the assist trophy route will always be more of an unknown for her to be playable in any smash game (no actual signs of actual deconfirmation) as that seems to the only viable route that she can be known to be HARD deconfirmed, or the Mach Rider music situation.
Lip's Stick item and Lip's Garbage Block was already known to not guarantee her a possible appearance in the game, so the view of discussion will overall be much different from other fighters. Its literally something that will never happen to any other character in any video game series, a reference for them can be seen as a hint towards a possible appearance such as the Namco items eventually which then Pac-Man came into the game. I know people who aren't familiar with this kind of discussion might just go straight to conclusion without any conclusive evidence. I especially see it whenever the Lip's Stick item is confirmed, the Garbage Block, and recently the Spirits/Mii Outfit.
I'm talking about it in the view that applies to any smash game for Lip, not just Ultimate.