Currently Fractals of the Mists consists of a series of unstable fractals that you’re supposed to stabilize. You get a random set of 3 each time you enter.
These fractals supposedly show (a version of) the past, and can if I’ve got it right show the present and future too.
But yes, fractals show the past and thus “fractal research” could be done to find stable fractals that retell the story that has gone past. For example the aetherblade retreat or the molten facilities.
So as these fractals are stable, you don’t get to them when you are stabilizing fractals, but instead, Dessa has created an archive of stable fractals that you can choose to visit in order to learn more about the history. That way they can be much longer and have different set of rewards compared to unstable fractals. It also wouldn’t make much of a sense to have them as unstable random fractals when you’re supposed to be able to replay them to learn more about the events.
Some rewards can be incorporated into this, like mist essence and fractal relics. Add back rewards such as the crafting recipes as drops from appropriate places.
To naturally fit it in with a living world… and with your development constraints… Ellen Kiel has revealed that fractal research towards a set goal is possible, and not just random search for unstable fractals. Thus it would be possible to do fractal research towards the lost living story parts. However, they can’t just come all at a time both for story reasons and development constraints. Incorporate them once in a while with living story releases with a note that Dessa has discovered a new stable fractal.
Simply rebalance the rewards for doing the content, add some commentary from Dessa or another special history researcher to tell what has happened. Then you can in alot of the cases just add the whole thing in just like it is.
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You could also use this to create hardcore (and rewarding!) “endgame content” that is designed to be of a certain difficulty as opposed to unstable fractals that are of a progressing difficulty and thus can scale weirdly.
I would personally like to see the Thaumanova fractal made in this way, but I do understand that development has already started for that and maybe you’ve thought of this idea already and are making the Thaumanova that way, or not.
Either way, if Thaumanova is introduced as a short, unstable fractal, you can later have Dessa discover a stable, longer version of it, telling more of the story.
And don’t forget the Abaddon fractal! We want it and you want to make it and we both know that
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Another note is that stable fractals could be used to recreate popular content from Guild Wars 1 in a new interesting way. Sure you can argue that "just go back and play Guild Wars 1 if you want to see it. But it would be interesting to play the content with 5 players in a rebalanced way as hardcore endgame content and that could also teach new people that haven’t played Guild Wars 1 about the stories from 250 years ago.
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So basically the stable fractals idea can be used as a platform to create both endgame content and to teach people about the history of Tyria from both long ago and from recent events.
My personal thought is that this would probably be the most interesting way of retelling the story and I think it would really fit with the world as it is now.