Ok, it's cool to keep Lodestar armor/syandana at 800/1000. Eventhou 3 years of uninterrupted logins is truly uncalled for.
One thing I would consider is changing the pacing of Milestones. Make them 25 day intervals instead of 50. While keeping the 800/1000 ones. I know it might be hard (impossible?) to retroactively give truckloads of milestones to every player thou. But if it were introduced as some sort of a "skill tree/timeline" visualization that you can access after the change instead of forcing you to pick 10 milestones at once on login. This would reduce the time to get everything gameplay related within 1,5 years while giving a reason to play for 3+ years still. And having a greater impact with evergreens.
Also the 'Evergreens' should definitely be available on 100 days and onward. Or 50 and onward if pacing is reduced to 25 intervals. This would make the proposed rotations more appealing in general. And I mean that when you get to 100 days Milestone; You are presented with a following example choice:
Also you should NOT BE FORCED to make the choice on login, but to have a choice to access the Login Milestone timeline/skilltree from Codex(?) and see how your choice will affect the upcoming options for next milestones. Aka; If I choose to take '4slots' on day 100, when will be the next time I can have access to Azima/Zenistar/Zenith or other RotA Evergreens? This is information I NEED TO KNOW when I'm making the final decision which item I pick. The game CANNOT assume that the player knows how the Milestone system is structured. It has to convey the information within the game before and after reaching the Milestone.
If the player has not progressed in game to have access to Kuva/Rivens these items should be shown as 'unknown' on the Milestone timeline/skilltree. Upon hovering over the 'unknown' milestone you are shown "complete The War Within quest to see this item". Ofc if you actually reach the Milestone which includes Kuva/rivens you can select them even if you haven't completed the quest yet. This scenario would still be highly unlikely imho. Or simply offer only Rotation A as evergreen until The War Within is completed?
If the player has not accessed the Milestone timeline/skilltree before the first Milestone, the player should be introduced to it right after.
There is a lot of opposite opinions concerning the Evergreen rotations. Some say that the values are ok and some say '3 forma is nothing' and 'I dont do anything with weapon slots after 1000 days'. Both sides are kind of right, because there is so many different situations progression-wise within the community. I think that changing the Milestone pacing to 25 days instead of 50 and introducing a timeline/skilltree would alleviate this issue. On top of making evergreens always an available choice after 2nd Milestone.
The Scaling changes seem good to me. We just need more content and resource sinks. Not one time heavy resource sinks like weapons (Hema), but something related to gameplay mechanics. Crafting costs for weapons/frames this year have been reasonable. Something that keeps us playing different planets dynamically with purpose and intent.
I'm not saying to retroactively double my login milestones, I'm saying that when I started playing Warframe and if I saw that I need to login for 3+ years to have all the stuff. I'd have never installed this game. I did not nor do play this game for the grind. I play it because how the gameplay feels, the mechanics, world/lore building. It encapsulates something that Half-Life series do. Gameplay fluidity, control, immersion, puzzles. If there is good content to play, I will sink an unhealthy amount of hours into this game. If there is only the grind for the sake of grind - I probably only pick up the login rewards for awhile; while waiting for something to use my resources on.
Don't make the gameplay easier, make it more challenging while making the rewards more impactful. I'm eager to see the new Jupiter rework and Fortuna enemy designs in gameplay aspect. Remove/replace the low tier bloat from highTier/uniqueLocation droptables. Example: Void (Hepit/Ukko) droptables after U23.9 - just replace the mods with relics and a 3% chance of Forma BP or something that actually feels good to have. All this ties together with the Login system and how it feels to acquire. The login system needs to support/augment your gameplay.
I hope this feedback helps. For perspective: I'm currently at 1033 days, which is 2 days behind the theoretical limit of Logins with almost 6k hours on Steam.