I just finished rereading the books and I noticed the number 10 shows up a lot. There's:
10 books in the series
10 heartbeats
10 surges
10 KR orders
10 oath gates
10 lamps in the Oathgate
A 10 pointed star in the Oathgate
10 shard blade stances
In one of Dalinar's visions, it shows the KR wearing Shardplate. We already know that Syl can become a Shardblade, Shardspear, etc. Then why not Shardplate? And if so, would she be able to become both at the same time?
(1. My power would be to be able to make the air turn solid and back to normal at will. I would also be able to make pockets of air solid and throw them at people, as well as make it opaque. I would always have a bubble of solid air around me which would protect me from bullets, explosions, etc.
(2. My powers wouldn't work in space or in a vacuum.
(3.
I have a theory that Tindwyl is a worldhopper. In Well of Ascension Elend describes the patch on his uniform as having a design with an arrow or a spear. This sounds like it could be describing the symbol of Bridge Four.