In regards to continued use of the Smash Ballot, I think it's a nonissue. Many fans evidently still endorse the same first party characters that they always have, for better or worse, and the growth of social media has made certain third party selections more visible with time. Sakurai has clearly had no issues determining that characters like Sans or Dante are sought after without needing a ballot to back that up. Simply keeping it in mind to substantiate a couple longterm requests like I dunno, Isaac and Geno or something would not be the end of the world nor the exclusive way fan requests are acted on.
Back to that initial first party point though, I feel like most Smash fans have simply not chosen that many contemporary characters to rally behind in the same way they have continued to endorse BWD, Dixie Kong, Waluigi, Isaac, Skull Kid... Swamp's poll makes it quite apparent that many of these characters are still pretty much top of the line requests. So at least within more dedicated Smash communities, the Ballot is probably still somewhat accurate to community taste. Primed character additions like Tom Nook, Squid Sisters, Oatchi or whoever are probably not relying on this kind of data to be considered in the first place so I don't see it being particularly obtrusive toward a natural roster evolution.
