Lucha Underground is currently in its fourth season and if the show gets picked up for another season, then Pentagon Jr. and Fenix would work that fifth season. Last year the show was picked up for a fourth season in November 2017 so fans will likely know by November 2018 if there will be another season.
The show currently airs on El Rey Network and even if they decide not to renew Lucha Underground, there is a chance that another network swoops in. In that case, if there is potential for the series to be picked up before the duo's non-compete clauses end, then they would be locked into their contracts with Lucha Underground through 2020 and be unable to join WWE.
To further complicate the path of Pentagon Jr. and Fenix to WWE, Impact Wrestling is also on the picture. Konnan helped the brothers negotiate a pay raise with Impact for a series of dates in 2019 based off the success of their appearances in the promotion earlier this year.
Pentagon Jr. and Fenix also have dates back in their home country of Mexico with AAA and CMLL, as well as indie dates in the United States.
The brothers are staying busy and seemingly working with every promotion outside of WWE. Time will tell if there is still interest from WWE's side once the duo is available, but for the foreseeable future don't expect Pentagon Jr. and Fenix to be in WWE anytime soon.