It's very unlikely SE would ever do this because of how much additional work it would require and the potential problems it would create with random groups.

It would be a balancing nightmare. A level 80 toolkit is much more powerful than a level 60 toolkit. Both of those are more powerful than a level 40 toolkit and all of them are more powerful than a level 20 toolkit. They would need to separately adjust potencies for every toolkit variation where a new skill with potencies or that impacted potencies was introduced and they would have to do it for each dungeon. They would have to repeat the process every time the level cap is increased or toolkits have major changes.

It would likely lead to more kicks for new players as well since they'd still lack the enhanced toolkits. Right now, there's nothing to be gained by kicking a new player because they'd be replaced by someone with the same basic toolkit. With your system, a party could kick the new player and likely end up with someone with party utility to make it a smoother run.

Worst of all, it's not going to make low level dungeons any more interesting. They're still very basic with very basic mechanics that you would have seen many times already. Retaining access to your full toolkit isn't going to improve the experience enough to make it satisfying.

If you want to be using your full toolkit, stick to doing content your level. You'll miss out on roulette bonuses but you'll have a more enjoyable experience if access to your full toolkit makes that much of a difference to you.