Why does it say "days are coming"?
Radak: [The curses] were not fulfilled until Tzadok became Kohen Gadol (Melachim 1 2:35). 1
This is unlike Malbim (34), who explains that they began the day that Eli's sons died.
What is "v'Gadati Es Zero'acha"?
Rashi: It is cutting off your strength in My house, for You say "if not, I will take by force" (verse 16).
Radak: I will cut off your strength, i.e. length of life.
Malbim: You will lose your authority to be Shofet over Yisrael.
What is the meaning of "mi'Hyos Zaken"?
Radak: They will die as youths (Rosh Hashanah 18a).
Radak citing Sanhedrin 14a: It is a Chacham, like "v'Hadarta Pnei Zaken" (Vayikra 19:32). No one from Beis Eli received Semichah to sit on the Sanhedrin.
Malbim: No one from your house will be a Shofet, Zaken (Chacham) or Nasi in Yisrael. 1
Malbim cites Sanhedrin 14, but there it discusses only Semichah. Why did he mention Nasi? "Lo Yasur Shevet mi'Yehudah" (Bereishis 49:10) already teaches that the Nasi is from Yehudah (Bereishis Rabah 97:10)! (PF)