1.This is a perfectly acceptable ending for Kirito, so it is very unlikely. Most likely, Asuna will leave Kirito saying what a loser he is. And the last scene will be Kirito sitting in the dark in his room and the sounds of sex from the apartment next door.
2.Most likely, Kirito will find out everything from Suguha. And Suguha, having shown his yandere skills, will take Kirito for himself. This will be the NTR ending in which Kirito just agreed to be with Suguha. I think neither Liz nor Sinon Kirito is needed as a partner or boyfriend. Liz wants to dominate him, and wants him as a slave. And Sinon has her own motives related to the council 6.
3.You forget that Kirito is not very capable as a lover. Because of his weakness, no one needs him except Suguha. So polygamy is almost impossible. And you saw for yourself what I wrote. "The Happy Cuckold" does not fit into the current plot. Inoda hates Kirito, Kirito is not particularly supportive of Inoda. What kind of happiness is there?? No, no, no. Such an ending is possible if Kirito completely destroys Inoda, and introduces Asuna to the world of other men. Remember Kirito's 3rd dream! Everything is as it should be, but no one will hold Kirito, and he himself will hold Asuna's hand.
4.See above. Kirito is a shitty lover, and he has enough for one sexual act a day and then with difficulty. So "Kirito the whore" is from the category of fiction. Only in the form of DLC and only if a big wad of money is thrown at Fujino.