Those in the WWE Universe who watched WWE's most recent pay-per-view TLC were aware the card did not end up as originally planned. Both Roman Reigns and Bray Wyatt were unable to attend due to illnesses and last-minute replacements were needed.
In the case of the missing Wyatt, Finn Balor would end up squaring off against Wyatt's replacement, AJ Styles, at TLC and the WWE marketing team had to promote a dream match in a matter of 48 hours. The match came off well and Styles and Balor tore the house down, but it wasn't the only backup plan suggested.
Ryan Satin on Wrestling Sheet Radio reported the WWE pitched a variety of ideas and one reported pitch included a reunion of The Club, a faction that consisted of AJ Styles, Finn Balor, Luke Gallows and Karl Anderson. The group is regarded as the founding members of the Bullet Club—a faction that has become incredibly popular on the independent scene and in Japan, but was called "The Club" in WWE due to copyright issues with the name "Bullet Club".
The faction is so popular, whoever pitched the idea knew it would attract fans. So too, seeing the original members finally get together in a WWE ring and in a four-on-four tag match would have been a great move for Anderson and Gallows respective careers, while saving a Balor and Styles match for a bigger show that had time to better promote the bout. If the group really caught on, it was something the WWE could have potentially run with on further episodes of Raw or SmackDown Live.
Speculation is that Vince McMahon himself shot down the idea. It is believed his discontent with how popular "The Bullet Club" has become has irked McMahon to the point he's unwilling to give any promotion to the idea of a similar group. When Finn Balor was pinned cleanly the next night on Raw, it was taken as a signal McMahon was not happy Balor and Styles even made hand gestures that were known as symbols of the group.
One day, the WWE may change its tune on a "Club" reunion. It doesn't appear that day is now.