This is somewhat related to Sfia's post here ( https://forum.square-enix.com/ffxiv/...aring-in-FFXIV )
My general thought process behind this post was to follow these rules:
1. Minimize the amount of development work needed to implement the changes
2. Maximize the amount of possible gear sets and variety for players to pick and choose from
3. Not invalidate any piece of content while also making sure that players can still decide not to do content they don't enjoy
As Sfia noted, there's a lack of variety in the current endgame gear sets. This is a bit stale at this point considering how long it's gone on. But, to counter the point, developing tons of new gear is time consuming. The gear looks and stats all have to be designed by a team that is, frankly, probably already nearing overwork just to give us what we have now.
With that in mind, I suggest that all of the gear that starts a tier also have upgrade paths to the end of a tier. This means that crafted gear and normal mode token gear can be upgraded from their starting item levels (610 for Abyssos) to the maximum item level of that tier (630 for Abyssos) starting within the patch they are added in (X.0, X.2, and X.4 patches).
I also suggest that the alliance raid gear and artifact gear (the colloquial name for for the gear given out for free in each expansion) should also have upgrade paths towards the maximum item level, but one patch after a tier is introduced (so the X.1, X.3, and X.5 patches).
For the token and crafted gear, the upgrade path would be the same as the tome gear, but in increments of ten item levels, using the same tokens as the tome gear from the savage raids (and later the alliance coins).
Now, this does introduce the problem of potentially making gearing slower than it already is, but I'd also like to suggest a small change to the current drop system to alleviate that somewhat: the upgrade items that drop from savage should be locked in a similar way to how the token gears tokens are locked, IE that they continue to drop clear after clear until the player successfully receives one item, and then from there they can no longer roll on that item until the next week comes around. This should hopefully help with a number of gearing issues, though I do not believe it will work without adding more possible endgame gear sets.
Next, for the alliance and artifact gear, I suggest that they are upgradeable using the same system as the current augmented crafted gear system, also in sets of ten item levels at a time until they reach the maximum. This does mean that the artifact gear would take considerably longer to upgrade, but this would ultimately be a players choice to work through.
These alone are, in my opinion, excellent options that minimize the amount of developer work required to increase the number of gear sets for endgame, while increasing player interaction with all content, including the alliance raids.