Honestly speaking I feel like due to the theme of this Event with all the new Small-Ships coming out, I think the Final Boss will be similar to Kitanda, basically a Destroyer but has the stats of a Battleship and above.
Whether it will be based off Suzutsuki or the Royal Navy DD will depend which map they are Reward of (I think the Royal Navy DD will be MO reward and Suzutsuki will be EO reward, but it could be vice-versa).
Well u are a bit wrong on power lv matter. Normal Abyssal BB (except RU kai flag) are no that great and lose to almost every single Hime out there be it DD or CV. Its also not ours BB lv cuz.... well.... don't think Yamato will get to 200 armor while im still alive... But don't worry Tanaka made it easy for u to know which one is which and now average new BB(V) Hime have 600-900HP while new DD Hime usually have 150-200 armor (still more than Yamato), 200HP and opening torpedo. So whenever there will be Kitanda or Kitanda 2 or Royal DD she will have average ABYSSAL stats :)
I am saying the new Boss for this Event will most likely be another those nearly ~300 Armor Boss with High Firepower, Anti-Air and Torpedo stats.
and thats just average new abyssal (Hime) stats these days so nothing surprising :)