meyrsTer: 1) If you are against DLC in the past, would you change your mind in the future if DLC actually gives hours of content for example the Witcher 3 season pass which allegedly would give another 30 hours of gameplay?
Those were called add-ons and/or expansions in the past. Now, with digital distribution, it's also called DLC, same as the infamous Horse-Amour... Expansions are fine though.
2) If you bought a pre-owned game and the former owner bought all the DLCs, for you to enjoy its DLC, it is required of you to purchase it again, would you buy it or do you consider the former owner should transfer all the DLCs to you?
What use has the previous owner of the DLC, when they don't own the game any more? Strange question.
3) Would you consider buying a short (less than 2 hours) story DLC to finish the story, especially if it ends on a cliffhanger?
I would consider a game that requires you to spend more money to see the proper ending shit in the first place. I would only buy some Complete Edition or GOTY in this situation.
4) Which do you prefer, short story and high replayability DLC (example: Burnout Paradise DLC includes new area to explore) or low replayability with a good story (probably just to finish and experience the ending).
See my answer to 3) for "to experience the ending". In principle both can be well done, so I don't have a preference.
4.1) If your answer to 4 is "It depends", then how do you determine the value of such content? How do you value the worthiness of story and replayability?
I could write an essay here... there is no simple answer.
5) Does having platform or retail exclusive DLC actually felt rewarding?
No.
6) If your best friend(s) own a DLC (or season pass) and you don't, for example in Battlefield 4, would you felt "peer-pressured" to buy it since you cant play on the DLC maps with him/her?
I don't play MP. But I'm kind of a completionist, so I'm always tempted to buy all DLC (and artbooks, soundtracks) for a given game. That's why I prefer Uber Complete Deluxe Editions in the first place.
7)What is your take on Subscription Based DLC which is reportedly in the works for games like Guitar Hero. What if subscription based DLC in the future made their way to be in games like Battlefield and Assassins Creed.
Since this can only be done by using DRM - not interested.
8) To those who play Train Simulator, how do you justify buying those DLCs which amounted to £3000+
Not applicable to me, but I know someone who spent 10,000 hours in MSFS with tons of (paid) third-party add-ons. So I guess the playtime/price ratio is not worse than "conventional" games.