The current monolith system is tedious. It takes ages to unlock empowered timelines and you have to do it all over again on each new character. This ruins what would otherwise be a quick and smooth levelling experience.
The current system also lacks clarity. Some timelines give you a choice of which timeline to unlock next, but it does not give you any details about those timelines other than their level (not even the name!). It also does not tell you which timelines you have already unlocked, opening up the possibility of time-wasting accidents. You can see this information on the map, but not at the moment when you have to make the choice. The game also gives you little indication of how to unlock empowered timelines. It just kind of happens by accident unless you look it up outside of the game (finish the last 3 timelines then touch the glowing rock).
My proposal is thus:
(assuming a fresh start)
At first you only have one timeline available.
When you complete it, you can choose another timeline to unlock. You can choose from any of the available timelines. The name of the timeline is clearly stated, as well as its special rewards (such as which unique reward nodes can be farmed there).
Completing a timeline also unlocks its empowered version.
The level of normal timelines would scale with player level up to a maximum of 90 and down to, for example, 60. Empowered timelines would begin at level 100 + corruption as they do now.
Regular timelines are shared across all characters. You only have to unlock them once per league/season/whatever they call it. Empowered timelines are not shared and have to be unlocked separately for each character. This cuts down on the “done this before” grind while still giving new builds something to progress through.
This lets you quickly reach the timelines that you want to farm without having to potentially complete several other timelines first (that may offer rewards your build does not care about, making those timelines nothing more than a necessary chore).
It also makes empowered timelines more accessible, meaning that the main barrier to entry for empowered timelines is the strength of your build rather than your willingness to slog through the same chain of timelines you have done many times before. The initial difficulty of empowered timelines could be adjusted if people begin completing empowered timelines too early into the game (if the devs care about that). Being restricted by your strength instead of by a grind requirement feels much better, since accumulating power is a core part of the ARPG experience.
There would still be substantial grind if you want all the blessings, but that’s fine because giving people a reason to grind and to complete every timeline is pretty much the point of blessings anyway.
Finally, it would be easier for them to add new timelines with this system because they can just add the new timeline as another unlock option. With the current system adding new timelines is awkward because it means expanding the web of timeline islands, extending the grind even more.