Personally, I think it's a good idea to find a way for people to "catch up", as I rather you keep working on Warframe than having to split off into a new title (like Destiny > Destiny 2). Meanwhile I think what you talked about on the devstream about not wanting to have people skip the best content is a very good point, but I'm also not sure what your plans/ideas are if people were to skip, would they have maxed Warframes/mods/weapons avaiable as well? And what about parts where you make a permanent choice (New War)?
This is coming from a LR3 player who won't be affected by this, but I think it'd potentially be a good solution:
A Bundle that gives you a built; Railjack and Necramech and a good selection of mods for them, along with some for Warframes and weapons. In addition to this, incl. a couple of tokens that can be exchanged for any Warframe that also can be farmed via The Circuit. And give them a selection of weapons.
Rather than have them skip the main quests, you create a "Golden Path" option, where you only need to do the absolute necessary quests. For the sake of the people starting in 2023 and onward, it might be worth shifting some of the main quests to side quests, to make the path more focused.
The New Strange, Stolen Dreams, Chains of Harrow, etc - not saying they're not important, but I think an argument could be made for having them as side quests as a "they flesh out details", but for the sake of creating a clear and shorter golden path, shifting these around would help folks reach Whisper in the Walls.