I do not think they will increase user level or Dino level.
User level is difficult now due to how much XP players have accumulated past hitting 20. Do they just add what has already been accumulated to the current level? Then you have instant level 31, 32, 35 or 40 level players. If they make everyone start from 20 and accumulate, you have a lot of angry users due to spending and leveling up everything already.
For Dino level, they could add more layers to them. The cost has an established pattern that is pretty linear. For example: Level 31 for a Common would be 100,000 DNA and 300,000 coins. I do not see it happening as the return on investment goes way down, it gets extremely expensive for those levels compared to what you gain.
So I see user level 20 and Creature level 30 as the max in the future.
Ludia will continue to add creatures and hybrids into the mix for users to create and level up. Some will be meh, but I see more being meta relevant. Speaking of meta, it will keep changing so the relevant creatures now, will be replaced with others. Some will remain top members for any team throughout the life of the game. But users will need to dart or battle for new relevant DNA. I do not watch the JP movies but I think they might add Dino not in them, such as another Rex hybrid so that Rex DNA can still be valuable even if users have a max level of all current hybrids. I do not see Ludia increasing DNA storage to help users accumulate more for when that time comes.
I can see them adding a new level of Hybrid at level 26 that would require components to be at level 25. That would keep users busy darting and leveling up Common, Rare and Epic. If you have a Common or Rare at level 20 with max DNA it would go to 25 with none to spare. I think you would have extra Epic though, not sure if I am remembering that table correctly or not. Forgive me if I am incorrect on that. A common DNA fuse for a level 25 hybrid might be 5000 or more DNA per. That creates lot of user time playing to create them!
They will also expand on the game mechanics to keep users interested. As we saw with Alliance missions, more alliance competitions will be added. We will also get more features rather than higher user or Dino level.
These are just the thoughts of a casual gamer. The hard-core gamers may see things differently.
EDIT: My bad. I was thinking of coin costs when I mentioned DNA for level 20 to 25. If you have a level 20 creature with max DNA it would be more than enough to get to level 25 and possibly have enough to create a possible future level 26 Hybrid, depending on that fuse cost.