Do we need another fork or LN can be added on top of Bitcoin blockchain so we don't need to change the rules?
No change needed, all you need to do is pay hefty Bitcoin transaction fee when opening and closing LN channel. You can imagine it as paying big fee whenever you want to load your debit card with a ballance to be able to use it for fast and cheap microtransactions. The point is, most people worldwide cannot afford such big Bitcoin transaction fees to open and closing LN channels, but fortunatelly we have Bitcoin Cash which is aiming to solve the scalling issue in different way which I think going to work better for normal people, thats why I dont care about big Bitcoin transaction fees anymore because I dont use Bitcoin anymore (just holding Bitcoin for price speculation).
I don't trust bch. It seems to me that the attempt to drag the blanket over the collapse for those who invest in bch. I don't know where to watch the developers. They can't solve this problem? Why splinter bitcoin bch maybe? Blackmail miners can only be overcome by economic means. A large number of transactions can increase income. Will always be willing miners if it is profitable.