According to an article from Pro Football Talk, the NFL owners will vote soon on a proposal to loosen the strict jersey number by positions rule. The main implication of this proposal is that it would allow a new group of players to wear single-digit numbers in addition to kickers, punters, and quarterbacks.
The proposal would allow running backs, fullbacks, wide receivers, tight ends, linebackers, and defensive backs to wear any number from 1-49, and for the aforementioned offensive positions, they could also wear 80-89. It changes nothing for all other positions, like QB’s who would still only wear 1-19 or offensive linemen who would still only wear 50-79.
The article also mentions that linebackers would have the option of wearing 1-49 and doesn't mention if they can still wear 50-59. Of course, the number 54 will be retired in a few years by the Seattle Seahawks as Bobby Wagner has donned it since 2012 so it would be interesting to figure that out.