Source tweet by @purusaa (Pulsar)
Thanks to Pulsar and Nether from the Taiko no Tatsujin Discord for the info and screenshots!
Aside from the paid DLC added today, Taiko no Tatsujin Nintendo Switch Version also dropped an unannounced minor version update of Version 1.2.3, which added additional ranks to the Online Ranking Match mode.
Before this, the maximum Rank Points one can get is 3000 which lands them in Rank S+. Those who have reached the cap can now play on to get numeral subscripts to the rank, starting from Rank S+2 and so on. The highest rank we currently see is Rank S+9 at over 4700 Rank Points.
Source tweet by @nether_fraud (Nether)