Just baseless speculation on my part, but...
I'm going to guess that the immortality chip has a dark side, namely that it grants immortality by eventually transferring the consciousness on the chip to the person it is implanted into, to the extent that the receiver's consciousness eventually gets completely overwritten and replaced by the personality on the chip.
The chip was probably intended for Saburo Arasaka, as part of Yorinobu Arasaka's quest to undermine Arasaka by implanting Johnny as a Trojan Horse, before V and Jackie throw a wrench in the works by stealing it and plugging it into V.
I'm guessing that the chip is ticking time bomb and that both V and Johnny will be on the same page eventually about uploading Johnny elsewhere, though Johnny is going to have his own agenda that may not necessarily align with V's. If Johnny and V have different goals I would not be surprised at all if he attempts to manipulate, use, or betray V in some way.