Legendaries serve two main purposes: removing level 80 materials from the market and providing a long term goal for players.
However, I think with the RNG/random luck of getting a precursor at this point, it is less of a long term goal and more of a pie-in the sky/grind CoF for hours and hours type of goal.
I propose that players be able to get a precursor by first finishing a subset of a list of requirements, like the current daily system. Each requirement should require a serious time investment. For example, some of the requirements could be:
1. Gain XX rank in WvW.
2. Gain XX rank in PvP.
3. Craft XX number of top tier Mystic Forge weapons.
4. Finish all dungeon paths.
5. Reach XX level in Fractals.
6. etc.
Then once you finish so many of these requirements, a second story line opens up. This story would be about you getting the precursor for a Legendary weapon and, as part of the story, you would pick which precursor you are going for. At the end, you get a precursor.
For those worried about the “precursor market,” all A-net has to do is announce this system a few months in advance and let people get out of the market before prices drop too much.
You could use this method to get a precursor once per account.
I know the story idea isn’t new, but I think this suggestion meets the original purposes of the Legendary but also allows dedicated, long-term players to have a more navigable path to getting a precursor.