I've just finished a Ryunohige myself recently and I feel like I should share the experience. I took 13 months from when I turned in my Radiant Lance to Naja's sad sack lackey, but the task wasn't a serious one until I get to Duties, Tasks, and Deeds. Everything prior to that was just completing content. Obviously the biggest part of making a mythic will be collecting the Alexandrite, but depending on how diligent you have been with ToAU content, it may or may not be the most frustrating. What I've read from many people who undertook Mythics before me was this: don't even consider it until you've gotten Captain. This really is no joke. I may be mistaken, but Captain also requires the completion of the ToAU storyline, so there's a whole lot of prerequisites.
To me, the worst parts of a Mythic were Einherjar/Ichor and redoing Assaults. Don't get me wrong though, the Alexandrite was bad, but the other two were by far more frustrating. I was not very active in attending Einherjar prior to starting the quest so this really bit me on the ***. This was before being able to buy Odin entry items, 20 hour cooldown, and renewed interest in Einherjar with Odin's Chamber II. So I had to find a small group that was interested in getting old gear or who were just generous to offer help. And before the Devs had even announced any adjustment to Einherjar, the prospect of quickly accruing Ichor was stonewalled by needing 9 feathers and a 72 hour cooldown. Starting from 1k Ichor on top of the alexandrite you knew you had to collect made the entire thing seem endless. I made it up to about 80k ichor before Einherjar was changed to how it is today. And the reason Assaults sucked major ***, besides the obvious, was because when I got my record books, Nyzul Uncharted was just released and everyone wanted to spend their Assault tags on that, and while it was new NO ONE was winning that without cheating, so you'd be lucky to see a single alexandrite from those runs. I was already done with my Wyrmseeker, but if you'd only climbed Nyzul to get your key and weapon, you'd be behind on tokens too, not to mention token cost of doing NNI as a DD.
While making a mythic now is easier (not dynamis revamp easier) it's still a VERY long quest. Some strategies that I did that I could offer to keep yourself sane is this; Do some dynamis for gil. Sell everything you make from there, put it towards buying Alexandrite. The biggest factor in finishing is staying focused. There were periods where I would impulse buy heavy metal plates for my empyrean that I immediately regret buying because the 90-100k per plate could have been saved to buy alexandrites should they ever pop up. The market on my server is flooded with alexandrite atm, much more favorable than within the 9 months I was heavily buying alexandrite. Make some friends, those who are willing to let you take the drites for the quest, let the cynics come out here, but they do exist. The way I see it my friends were very kind to put aside their immediate need for gil. Find people who are also willing to snatch up alexandrites for cheap should they ever catch some undercutters when you cannot play, and do whatever you can within your power to pay them back immediately. I am proud to say I never owed any huge debts to any of my friends up until my last few thousand, where my biggest supporter would force me to up my pace. In the end I would owe him 35m. There's two and a half events that now provide a source of Alex. NNI that is easily won with a group that knows how to work well together, Salvage II that can be trio'd very successfully, and Original Salvage (Silver Sea Remnants) that can put out a considerable amount. NNI is a linen 100% per every floor 100 win, and a very slim chance of seeing cottons per boss floor prior. Salvage v.2 is guaranteed one linen per HQ boss and a small chance and a first linen from the 2nd to last floor NQ boss. SSR gives 4 guaranteed cottons and a small chance at a linen. Knowing what to do is half the battle. With this strategy, I spent an estimated 160m in making my Ryunohige to 75. I could have kept better records to tell people how many Alexandrites I actually paid for vs. how many were donated or personally farmed from Salvage, but I didn't. Oftentimes just seeing the number you need to turn in just makes it demoralizing. I kept count by counting them in stacks. That's approximately 304 stacks of 99. It might not be much, but it might help keep you sane.
I ended up writing out a lot more than I originally intended, but that's only because I wanna put it out there that this whole thing isn't as nearly as impossible as many people make it out to be, especially considering that I did this without the official backing of a huge EG linkshell -- the LS I'm in now I joined when I was about 60% done with D,T,&D so if anyone goes and checks my FFXIAH profile there's no need to call *** lol, I did in fact do this with only 4-5 of my closest in game friends. It's Lv. 99 now, and I will tell you straight out that Ryunohige is easily, in practice, the best polearm in the game. While on paper Gungnir might be better because of base damage or whatever, Ryunohige really does some jaw dropping things. Sorry for being long winded, but best of luck to anyone who attempts this. I hope sharing my experience with it was in any way a little bit inspirational. I couldn't be happier with this weapon.