The tweet asked,
Do you believe that in 10-15 years we'll be able to know the "truth" about the major opening lines?
It's a good question for GM Svidler, who also has top-level knowledge of chess960. See, for example, No Place for Chess960, for his chess960 accomplishments at Chess Classic Mainz. The GM answered,
PS: If by this you mean the complete truth which will actually change the way people play chess because it will not be possible to play certain openings because the answer will be known and everybody will be able to reproduce the answer at the board, the answer to your question is 'No'.
SG: Chess will die in that case.
PS: Not really. First of all, I think the heaviest research and work which can result in what this question was about... It's being done as was correctly pointed out in major opening lines. Nobody really spends -- I'm saying 'nobody' but this is probably a mistake -- but not too many people will spend time, effort, and energy getting to the bottom of (I don't know) the Morra Gambit or something.
Generally, theory moves in leaps and bounds in lines which are fashionable at the moment, which are played a lot by the current top players, because there are trendsetters and there are people who just follow the trends. When the trendsetters suddenly begin playing a certain opening, that opening starts attracting a lot of high level games and this way theory suddenly progresses. In a very short period of time you get a lot of new stuff known about the opening. But that only applies to a select few openings.
Secondly, if you're willing to play slightly offbeat lines I don't think it's possible to completely close down chess for good by advancing opening theory. Also there's a question of memory. Let's say if we assume that somehow, let's say the mainline Gruenfeld, becomes solved in 15 years it becomes a question of can you actually remember the answers to all the questions that the opponent can pose you. It's a huge opening and even if you feel someone has come up with an actual answer to whether it's winning for White or a draw, the amount of memorization involved in repeating all those lines is almost impossible.
SG: Black also has so many options you have to memorize all of them.
PS: So, first of all I don't think it will happen, and secondly the impact on the actual playing of the game at -- in particular -- amateur level will have almost zero impact. Apart from discouraging some people from taking up chess, but even then is not a huge factor. Anyway, I think we've spent a bit too much time discussing the doom and gloom...
Although Svidler didn't mention chess960, I imagine the idea crossed his mind as he was answering the question.