Dryone

I missed that! Yes, that totally sounds like one of the cover charts. The interesting questilon is if it's the Heralds' or the Voidbringers'...

I like it. In fact I had similar ideas, but not in so many words.

I think that what the Allmighty's shard represents (Creation? Life? Transformation?) is loose after his death and manifests itself as spren whenever an opportunity arises.

But Syl might be different. In one of the visions someone says about a Knight Radiant/Surgebinder that he has the "Nalan(sp?) bond". So apparently this bonding was possible before there were spren.

You are right, I can't find any mention of female heralds. At least two of the heralds faces in the chapter headings look feminine, though (at least to me. But I also thought that the picture of Nalan'Elin depicted a woman).

OTOH it nowhere explicitly says that all heralds were men, either. So I stand by my theory! 

I don't buy the Lerasium theory. I think the element is the body of another shard which was bound to the writer of the letter. Or he stole another shards body? Maybe Bavadin's?

Not for sure, but it sounds like a female name to me (cf. Shallan, Hashal)

We do know there were female heralds, though.

It's Shalash, one of the heralds. She's destroying all pictures and statues of herself, that's why her statue is missing in the prologue. Apparently she's revered as "Lady of Dreams" by the Emul.

It also explains why Baxis can't decide her race.

Thought's?

Talenel still being around, though, isn't proof that the others still are.  Remember, just by virtue of having died, Talenel didn't break the oathpact.  He's been living (dying? not sure how to put this) in a state of continual torture for the oathpact for the past 4,500 years, so it seems to me that the others could all be safely dead, and Taln would still be around.

Talenel hasn't been around, he's just coming back Poor guy.

Someone said that Axis the collector might be one of the other nine. After all he has a quest that will take another few centuries...

Another candidate is the mistress. Both show a slightly mad behavior which could be caused by the torture or their guilt.

So my guess is some or all of the nine are still around.

Numbering your possibilities, Munin:

1. Jezrien

2. Talanel

3. The Almighty

4. Odium

5. Bavadin

6. Hoid

I think it was neither of them, but Cultivation aka Nightwatcher.

a) The voice is all in caps, so it probably not human (ruling out 1, 2, 6).

Odium is unlikely since the voice warns about him

c) The Almighty is dead, and this doesn't sound like one of the recordings.

d) Bavadin - not much information on his one, but I guess he's not on Roshar

Pro Cultivation/Nightwatcher:

e) The voice appears at the west coast of Roshar. Old Magic is also sought in the west.

f) My theory is that the 3 shards on Roshar are Odium, Almighty and Cultivation. Odium causes wars, the Almighty is responsible for Stormlight (and probably the highstorms) and Cultivation makes the soil and strange plants in the west (and the Old Magic)

It might be the mechanism how spren can be caught in gemstones. Also reminds me of lasers.

A dragon?  In Dragonsteel?  ....  Not that I remember.

I think I read that there used to be a dragon but it was removed from the final version because it wasn't needed. IIRC some answer to an interview question.

"You might say I protect it like my own skin" could also mean he made the element part of his skin or someone other's skin. Parshmen and Elantrians come to my mind.

I read somewhere that there was one Dragon in Dragonsteel, but he wasn't a pivotal character. So my guess is that the letter is to this Dragon, who is probably a shardbearer. At least that's what I thought when I read "old reptile"; and saying "old reptile" instead of "dragon" could be considered even witty.

Sazed's name should be obvious: Hero of Ages.

It says so in the first line of Mistborn: FE