I hope that instead of adding more skills / actions, the devs make the new skills "overwrite" some old ones.

This is just a totally hypothetical example to illustrate a point. Let's image the spell "Stone".
Instead of creating a Stone II, Stone III, Stone IV, Stone V, etc and having them ALL on the hotbar because they do different things and are needed at different level syncs, let's take "Stone" (or any upgrade of "Stone") and instead of adding the next tier spell as a separate spell, make us learn a Stone "upgrade", so "Stone" gains an extra ability, potency boost, or effect.

If we are level synced, it would remove that effect for that dungeon.
Once we get "Stone II" we never use "Stone" anymore unless we are in PvP or level synced. The same is true for Stone III.
Why not simply overwrite Stone with Stone II, and when we are level synced it automatically reverts back to Stone?

This could solve the cluttering problem.
We wouldn't have super cluttered hotbars. I wouldn't need to keep Stone, Stone II, Stone III (and in the future, Stone IV) on there because I never know what level synced dungeon I'm going into. One "Stone" which scaled depending on the level sync would suffice!

If they were to implement an "upgrade / overwrite" system, we would just use the downgraded version of that spell or ability when level synced and wouldn't need to remove / switch so many things.

Even now I have 3 hotbars just got all my WHM spells, plus another hotbar for potions and food.