I was going through these changes and I have some comments:
1.) Fiery Brand use - I tried out the changes you recommended... but I don't see a change in DPS/NPS/Death Chance either way compared to just using it on cooldown. I don't understand what you are trying to do with this condition:
SecondsUntilBigHit > CooldownSecRemaining(FieryBrand)
This will effectively cause Fiery Brand to be used on cooldown whenever it is available. The only time you can use Fiery Brand is when CooldownSecRemaining = 0, in which case SecondsUntilBigHit will always be > 0 and evaluate to true. I tried out a rotation with what I think your intent was, which is holding onto it for a big hit unless a big hit is far enough away that it will be ready again. It didn't really change anything, since "big hits" are frequent in the simulations.
2.) The Empower Wards change seemed to be a good one with the legendary on, so I added that into the default.
3.) The amount of pain being wasted with the default rotation's use of Demonic Infusion was negligible, but I added in a check for it anyway to satisfy our OCD. I don't understand why you'd use Demonic Infusion with a charge of demon spikes left even with the legendary pants. Seems like a waste of a demon spikes charge to me. I tried it and the results were within margin of error either way, so couldn't really tell if it mattered or not.
4.) Using Spirit Bomb at 4+ fragments instead of 5+ fragments is a change I had tested before. It results in the same amount of survival and the same amount of DPS. I can change it to 4+ to match what folks are doing in logs better, but it really doesn't matter either way. You might get a hair more damage by using it at 4+. I also tried the change with respect to soul barrier... but that was yielding far less damage and survival when I tried it. I don't understand the logic behind that change, so we'll have to discuss that further and see if there is an improvement to be made.
5.) Using Fracture at <= 4 instead of <= 3 seemed to have no impact on the simulations either way. I can add it in if that is what people prefer.
6.) The change to use Fel Eruption only with razor spikes seems to be a slight DPS increase, just barely out of margin of error range, but I can add it in if that is preferred.
7.) I added in better use for the legendary hands like you suggested. I tweaked it a bit, though. I found that if I focused on getting max use out of the heal component, I got a nice boost to survival. If you are simulating against trivial content, you'll see a slight DPS decrease because fiery brand won't get used as many times as it could, but, against difficult content it was pretty solid. Arguably you wouldn't use that item against trivial content, so I think this is ok.
8.) A change you made was moving the soul cleave much lower in the priority list. When doing sims for content that is tough for the player, I find that the death chance spikes significantly when you don't have that soul cleave taking priority over fracture. I know a lot of veng players don't ever use soul cleave at this point... but all the simulations show that you will significantly lower your chance to die if you use soul cleave when you are below 50% health. You lose some DPS by doing this, but, it really matters. 4t20 makes this even more worthwhile, obviously.
Once I push this live, I'll do another comparison between the new default and your edited rotation. You changed the priority of a number of spells, so I still have to test some of those out.