Unfortunately, the last Dev I talked to said they had no plans to increase level caps, but I feel like that's not the best approach. In a game where being able to brag about how strong you are has merit, it would make sense for players to guage strength based on level. The rewards don't have to much, but it's nice for players to always have something to look forward to even of it's something as small as more coins.
Some may argue that that's what rift tier is: a bragging rights system that gives great rewards. But this would be for all players regardless of rift participation, and can demonstrate how good their fighters are on a more universal scale.
Higher levels would also help pinpoint cheaters. They may make it to a high rift tier, but their raw exp will be more accurate as to how good their fighters actually are/how much they truly play.