The GOAT LW yes, but I wouldn't compare him to GSP, Silva, Jones, DJ or even Cormier or Aldo. I believe to be called the GOAT you need to consistently fight and beat the best for a while and it's something just the few I have mentioned above, have been able to do. The trend is to win the belt, defend it once and claim you're the GOAT.
I think Khabib can already be considered the best LW ever, but his fight with Ferguson needs to be settle first. One could argue Ferguson has a better resume than Khabib right now. Assuming Khabib defends his belt against Poirier and Ferguson, without a doubt, he is the greatest UFC 155lbs fighter/champion.
When it comes to the P4P GOAT discussion, Khabib is going up against fighters with solid accomplishments.
I don't think a win over Poirier and Ferguson is enough to claim he's the best.
I'd love to see him move up to 170lbs, he is a massive 155er and he has big pay days waiting for him in that division.