A recent episode of The Flash revealed that Team Flash had unwittingly laid the groundwork for creating the future Flash Museum through their creation of the "Starchives". Though a minor point in the episode's larger storyline, this revelation suggests several things about the future of the Arrowverse.
First appearing in the comics in The Flash #154, the Flash Museum was created by the people of Central City as a tribute to their hometown hero. The Museum's existence in the Arrowverse had been hinted at in earlier episodes, but was more fully fleshed out in The Flash season 5 as Nora West-Allen spoke about how she used the museum to learn about the father she never knew. Some of the museum's exhibits were depicted later in the season, with Barry Allen getting the chance to see a part of it for himself in "Memorabilia."
The Flash season 7 episode 17, "Time Bomb" introduced STAR Labs' Starchives, secure facilities where the team houses everything related to The Flash they needed to keep safe but didn't want underfoot, including old costumes, prototype weapons and advanced devices such as Eobard Thawne's Time Sphere (this last item is the subject of the episode, with it stolen across time).
Though the scene where Iris and Ralph explore the Starchive to make sure it hasn't been robbed is brief, we do get a glimpse at some classic Flash history as they move around to where the time machine is stored. Barry's old costumes are visible in the background along with several one-shot weapons used in previous episodes. While none of these items have been visible among the brief glimpses we've had of the Flash Museum, the fact that the Starchives exist at all offers an explanation for where its exhibits came from.
The existence of the Flash Museum also offers a hopeful view of the broader future of the Arrowverse. Most of what we have seen of the future hasn't been happy, with a fascist government taking over America and outlawing superheroes and religion in the alternate future of 2042 that gave birth to Zari Tomaz. There's also the dark future of Star City 2040 that has dominated Arrow's season 7. The idea that one city cared enough about its greatest hero to build a monument to honor him and his idealism is perhaps the best thing to come out of any alternate Arrowverse future we've seen so far.
Though the details of exactly who founds the Flash Museum and how it comes into being have yet to be revealed, it seems clear that The Flash's friends will have a role in crafting its exhibits. This may prove to be an important point given the approach of Crisis on Infinite Earths - an event that did not originally end well for Barry in the comics. Still, if the Arrowverse version of The Flash is destined to die a hero's death this fall, we can take comfort in the fact that he will not be forgotten by the people of Central City.