Lucci has no deams, his only pleasure in life is killing people (the thing the WG allows him to do without consequences) and thus cannot become a SH.
Many people think that his goal in life is to kill, but this is not the case:
Let me explain and differenciate something:
Lucci was never portrayed as brutal and dark, nor is he a sadist. His sole priorities can be summarized in one word: Duty. In his mind, fulfilling his duty comes first before anything else. He always puts his orders/missions as a priority, towards which he works with precise accuracy. There is no place for empathy or warmth, nor for friendship (Pauli) and weakness (500 soldiers). It doesn’t make him brutal, but only cold.
The only times he diverted from missions was, when he wanted to have some fun (turning into a Leopard-human-form in Iceberg’s office; letting Chimney follow them) and was sure those slight hedonistic tendencies were not jeopardizing his missions. Because, in his thinking at that time, they did not contradict with his given orders (getting the pluton blueprints; protecting Spandam).
I think, it is a way to give himself the room for his own enjoyment, solely because he wants to have some fun fighting someone. It is also the same reason why he often times tries to incite his opponents to fight him (Sanji on the Puffing Tom; Pauli in Iceberg’s office). Lucci loves fighting! However, up until Egghead, he never had made a move to endanger their missions in any way through his own personal drives.
What is noteworthy however is that he is very curious regarding interpersonal relationships and emphatetical motivations. Even if he had his difficulties understanding emphatical drives, he is curious and tries to grasps the concept of it, when he comes across it in real life. That is, why he asked Franky why he was helping the Straw hats back on the sea train, but had his problems with grasping what the cyborg meant. It is also the reason why he wanted to know why Luffy was helping Pauli.
Then we have his motivation: During the Enies Lobby arc, Spandam asks CP9 what drives them, to which Lucci replies something along the line of “Blood perhaps, and as long as we are in CP9, we are even allowed to kill.”. The statement comes off as something Lucci is not quite sure about himself. Why else would he add the “perhaps” at the end? I wonder what takes him to the conclusion to say “blood”. Considering he is an agent that needs to draw blood during his mission, it would be understandable for him to say that, but none the less it lets room for interpretation.
All in all his actions were always driven by his responsibility to fullfil his duty, rather than his own personal interests.
Now, with the start of the Egghead Arc, however, we see his priorities somehow shifting (starting a fight with Luffy, questioning their orders). Sure is – he still is trying to kill Vegapunk as it is his order, but with his actions he is endangering their mission and the underlying factor as to why he does it I have a good answer - Shaka, his twin like counterpart. He is depicted to just act and talk like Lucci to a point, where it does seem crazy obvious if you once notice it. Try it - it's crazy!
Besides his goal is not to kill - it is rather the opposite: In an SBS a fan once asked, if Oda could draw the CP9 members as children. You know how he drew Lucci?: With an olive branch (symbol of peace) in his hand, Hattori - his white dove (symbol of peace) - sitting before him and with Lucci wearing a shirt with "Peace" written on it. No one else from the CP9 members was indirectly stating something underlying in that picture, except for Lucci.
There are many more of those hints throughout the story and with the current situation, I am now very sure he will join. You can trust me on this.