I think that a pay to skip is misguided. The quests themselves, while some could use a little bloat trim (looking at you, Natah) are not some long slog to get through. The larger issue is that you have only one, very in-your-face way to progress the game: the star chart. The star chart and junctions being the gates to the story are what slow folks down getting up to and through the New War, aside from the being-worked-on Necramech and Railjack acquisition. For a new player, after being guided through Vor's Prize, they are dropped in front of Navigation and the only goals immediately apparent to them are unlocking more nodes on the star chart and doing junctions. Aside from occasional voice lines from Lotus saying you have new quests and a fairly ignorable notification in the top right (all the side quests are baked in with these, no way to tell if "Howl of the Kubrow" is important story or not), the game only points you toward its awesome story as junction objectives. This puts a quest as involved and important to the story as Natah on the same level as "complete 5 missions with only your melee equipped."
Proposed solution: Story-focused Mode/Menu
A much better solution would be to have a heavy, in-game focus on the quests. Warframe already has a quest guide (https://www.warframe.com/game/questguide), and honestly if you had a menu that was "Here are the main story quests, in order, you can do these regardless of your star chart progression," then players could get through the story in a relatively digestible manner. It should be something on the level of the navigation screen-- like the Duviri or Railjack buttons on the navigation screen, but more prominent / some other way of ensuring that players see it. Maybe the game defaults to the Main Story menu when you access navigation until you've completed Once Awake, or some other fairly-early mission. Until then, there is still a button to swap to the star chart normally, and afterward you can still swap between the two. The point is to ensure players know and see that there is a lot of awesome main story and how to access it.
The story menu wouldn't unlock new planets and the story quests would not require junction completion to be able to access them. The menu could say whether or not the quest is solo only and convey the "here's kinda where you should be / what to expect on this mission" in the quest selection similar to the quest guide, with a huge first-time tip of "These are the main story quests in order, but you do not need to complete them all at once. If you find yourself struggling in a mission, explore the star chart to gather mods, resources, and blueprints for new weapons and Warframes to strengthen your arsenal before coming back!"
I think this would really help put more of a spotlight on quest progression, and along with some trimming of the fat in certain longer, repetitive quests, as well as streamlining getting a worthwhile amp, a Necramech, and a Railjack, the burden of "10 years of content before I can play with my veteran friend" would be very manageable and remove the 'need' for a skip. Junctions can still keep quests as objectives to unlock as general story-gates, but ideally players will have long completed them by the time they get to that junction.
My new-player anecdote:
I have a friend that I got into Warframe recently (started just after TennoCon), after touting its story. While she was able to get to the Second Dream fairly quickly, a byproduct of that was that she had no idea who the Stalker was. I made sure to covertly divert her to farming some other things before questing up so that she could get invaded a few times. We play friends only usually, so I was able to leave the Stalker up and let her experience the fight instead of him getting one-shot. If you don't particularly farm a boss for a new frame (never get marked), prioritize the story missions, and play public (Shadow insta-dies), you could very well not even know who or what the Stalker is by the time you start this quest. Maybe working him into another quest or something as an introduction to the character would help this.
It helps that I am in the same room playing with her, but there are a lot of times she asks who someone is or if she should know what something is. Everything with Alad V, for the most part (his story is so scattered across the star chart), Teshin showing up during Natah, people talking about the Dax, Tyl Regor's inexplicable sex appeal, etc. are all a mysteries / contextless to her. I steered her away from Deimos for a short while until she got through Second Dream because of the questions that arise with Transference swapping between frame and mech. We haven't got around to getting her a Necramech and RJ, since I advised her to wait for the Abyss of Dagath updates to that process and recipe, but in that time she's gotten much more powerful in mods and arsenal and even got her first Kuva weapon.
The idea that a new player would need to skip to play with a vet is silly. I can and do play SP and Archon Hunts and Zariman bounties, just not with her. If my low-leveled friend and I want to play together, we just play at her level. She wasn't swayed by a trailer for a big story update, so I understand that aspect doesn't apply in this case, but the half-dozen friends I've brought to the game all have been comfy playing at their level and haven't felt like they needed to be where I am to play together.
