"The Flash" episode of 28 April, Tuesday, titled "The Trap" was one of the most compelling episodes of the series, and not just because the Reverse Flash revealed his identity to Barry and his friends. Season 1 episode 20 was filled with clues of what the future holds, for Barry, Oliver and even "The Justice league".
The following calculated assumptions may contain spoilers:
Iris and Barry
The article itself speaks about the disappearance of The Flash (Grant Gustin), after a battle with the Reverse Flash (Tom Cavanagh) on the night of 24 April 2024. The article is written by the love of Barry's life, Iris (Candice Patton); only her surname is now West-Allen, meaning at some point in the future, she marries Barry.
Eddie's dark future
This future wedding would be heart-breaking for Iris' boyfriend Eddie (Rick Cosnett), who was about to propose to her, when the Reverse Flash attacked. Another revelation made in the episode, but was already known to comic book fans, is that Eddie Thawne is related to Eobard Thawne.
Eddie is merely insurance for Eobard's longevity; any harm to Eddie would disturb the Thawne family line, leading to the in-existence of Eobard. It is not official whether Eddie will join an alliance with the Reverse Flash in the future, but every arrow is pointing that direction.
Oliver Queen escapes League of Assassins
Speaking of arrows, the titular character of The CW's "Arrow" has been mentioned in Iris' article as the Green Arrow from Starling City. As per the "Arrow" series, Oliver Queen (Stephen Amell) has hung up his green hood and is now an apprentice of "Ra's al Ghul", or the Demon's Head. Currently known as Al Sah-him, Heir to the Dragon, he is expected to take over as "Ra's al Ghul" and lead the League of Assassins soon.
However, this article suggests that Oliver is able to escape from the League of Assassins and return to Starling City, and take back his rightful position as the green-hooded vigilante.
The Justice League
The article also mentions The Atom, played by Brandon Routh in "Arrow" and Hawkgirl, who is yet to make appearance in either of The CW shows. Denoting Oliver as Green Arrow instead of Arrow, as he is known currently in Starling City, and the mention of Atom and Hawkgirl, many believe, is a foray into the formation of Justice League.
The Justice League superheroes have constantly changed over the years, and Green Arrow, The Atom, Black Canary (Katie Cassidy), Firestorm (Robbie Amell), Speedy (Colton Haynes) and Hawkgirl. All of them, other than Hawkgirl, have been introduced via "The Flash" and "Arrow".
Below is an extended trailer for finale of 'The Flash':