Okay but why?
If your main metric for cutting characters is how old they are, you're only going to cater to older fans for the sake of it.
SSB seniority an interesting topic to discuss and its role in who ends up becoming a higher priority going into the next game. Here is my current position below, but I think this topic is honestly nuanced and complicated.
Seniority is not the primary determinant in who gets prioritized, and the best example of this is Jigglypuff, who barely scraped into Brawl and For despite being one of the originals. Also, there are newer characters who I‘d be shocked to see cut before long established veterans. The most obvious examples are Ridley, Villager, Isabelle, Shulk, Inkling, and Mii Fighters. Even though a character like Jigglypuff, Sheik, Zero Suit Samus, or R.O.B. has more seniority compared to the six above in the context of SSB, they’re absence would probably stick out less compared to those six. Losing staples can sting (think Waluigi missing out on Mario Kart 7), but we’ll be able to move forward.
Even though I don’t think seniority is necessarily a super important factor, there is one thing that I really want to highlight here:
SSB is not just a character selection screen of the most popular/relevant characters in gaming. Even though some older characters have a smaller gaming legacy compared to newer fighters, they’re able to contribute in different ways, which could be through their popularity in the SSB community or their gameplay mechanics.
In summary, seniority isn’t the only factor that matters in character selection, but I do think we also overlook a character’s prominence within SSB when discussing character selection.
Marth. The obvious first choice for Fire Emblem if Smash would release today is Marth.
I honestly think it would be a Three Houses character given the game’s popularity, but I would understand arguments for Marth, Chrom, or Lucina.