Idt he has ill will toward Shoto but destroying the successful experiment would hurt Endeavor...I mean it's not like he can have more kids with his estranged wife until he gets another one with a double quirk. It is sh!!ty that he thinks of his brother the same way endeavor used to...as an 'it/thing' instead of he/person/son.
the fact that he doesn't really see shoto as a sibling probably plays a role in that. dabi was able to spend his childhood with fuyumi and natsu but shoto was raised separately. as years passed by shoto was able to form a bond with both fuyumi and natsu but dabi was already supposedly dead by then. dabi's goal is to hurt endeavor in a way that matches with the pain he received. he still thinks that all endeavor cares about is surpassing all might with shoto as leverage. so "killing shoto" means killing endeavor. he doesn't know the emotional progress endeavor's been having. it's true endeavor will care about what happens with shoto but he will also care if any of his children will get hurt - dabi included (probably). so my theory is that shoto and dabi will have a battle with dabi aiming to kill shoto, but shoto will have the upperhand somewhere in the fight and dabi will get hurt then endeavor will feel remorse and run to dabi's aid then the drama starts from there.
HOWEVER, THE LITTLE GAY DANCE ASIDE, HOW IS SHOUTO AT FAULT FOR YOUR ABUSE HDUVOF HE WASNT EVEN BORN WHEN IT BEGAN DUMBAS... like ik hes blaming his abuse and trauma on endeavor and how shouto was the only one with a functional, powerful quirk but dabi i love you but man you really suck for targeting your LITTLE BROTHER who is a victim as well, ur weewee aint big enough to see past that