Theory: Homelander will want to become immortal like Soldier Boy, and the only way for it to happen is for him to be depowered and then get the original Compound V injected.
In season 5, Homelander will ask Sage to study Soldier Boy and understand why he is ageless and how to apply this to Homelander.
Sage will confirm a popular fan theory, that the original Fredrick Vought's compound V is a superior product to the stuff mass produced by the company today. Being a super genius she could replicate it, however using it on Homelander will not work since he already has the inferior V in his body.
The only way for Homelander to become the immortal god he sees himself as will be to have Soldier Boy depower him and then inject the superior V - Which means Homelander will be a regular human for a while, meaning anyone (Soldier Boy, Butcher, even Sage herself) can take him down at that moment of vulnerability.
This can make an interesting situation where Homelander is paranoid about whether to go through with this plan and who he can actually trust to have his back once his powers are temporarily gone.
Edit: The responses to this thread have confirmed my suspicions - The Boys fans never actually watched the show.
"SB isnt ageless, he was frozen"
SB was captured in 83. He was born in 1919, making him 64 before being captured. This also means he was ageless before the russian experiments
The russians used Novichok, a nerve agent / poison, to knock him out. He was NEVER frozen, just asleep.
The legend confirmed SB doesn't age, and that Vought had been covering up this fact.