Mayhaps I should shoot some questions into the dark since I'm already here. I'm pretty certain none of these have definite answers at the moment, but at least there could be some interesting tidbits that I'm unaware of.
1) Shard Powah!!! Are all Shards equally powerful? Ruin and Preservation were quite evenly matched but that doesn't really prove anything about others.
2) Shard Angry. Shard SMASH! The way I gathered from HoA, Shards are like balloons full of water floating around a planet. They can smash into and hurt each other. Since Ruin and Preservation were filled with equal amounts of "water", they destroyed each other's "drivers" in a full on crash. But if one had significantly more "water" would it kill the other? Seems logical to me, but who knows?
3) Shard pairs? Ruin and Preservation were quite neatly paired. I know Sanderson said not all Shards are so neat opposites, but that doesn't mean there aren't other pairs. Like Aona-Rayse. They seem opposite just like R&P to me, so would that mean their Shards are equally large? For all we know, 14 of the Shards are paired with last two different. Very unlikely, but possible. Therefore, are there other paired Shards like R&P?
4) Shardicide. Rayse has a pretty high bodycount among Shards. If my "water balloon idea" is correct, that'd mean his Shard is bigger than Aona, Skai and Tanavast's. But if it's not correct, there must be other ways to kill a Shard's mind than brute force smashing. What could that be?
5) Smash Hit! How does one go about Shattering a Shard? Do you have to kill its mind first then "violate the corpse" so to speak, or is hitting them hard is enough? Or maybe there's some way to trick and manipulate a Shard into Shattering?
6) Voidbringers, IN SPACE!!! Is there a need for mortal agents for Shattering or killing Shards and if so, did Rayse carry Voidbringers in his back pocket to Sel? If he didn't carry them, did he make more on Sel and where did those go when he was done? If he doesn't actually need mortal agents, why use them against Tanavast? We know for certain he defeated Tanavast after he stopped sending waves of his mooks upon Roshar, so a) He's always been "bigger" than Honor and finally killed Tanavast b ) Honor "deflated" after Heralds and Knights Radiant broke their oaths allowing Rayse to win c) Rayse "inflated" after his visit to Sel/broken oaths on Roshar d) Sanderson will surprise us. Considering Ruin's demise, mortal mooks don't really seem to do anything against Shards themselves. Whatever the case, Voidbringers being carried through the cosmere dangling from an ethereal hand as in Dungeon Keeper is too amusing to contemplate. (this one is rather full of random rambling)
7) Uncle Rayse's Shard Shattering Shop. Or could Shattering be a speciality of Rayse thanks to his Shard's nature? Now I know you'd say this looks like a job for Ruin, but I think if Ruin would have a speciality when it comes to Shards, it'd be completely disintegrating the power instead of just breaking it. Being "shattered" would presumably be a painful thing, so it's more Odiumy than Ruiny, especially if they're alive during it. Not that there's any proof individual Shards have such specialities of course. It's a slim justification anyway, just looking for an excuse to write URSSS.
8) Do we know how many more books there'll be until the end of "Cosmere Saga"? I know of 9 more Stormlight Archive, 6 more Mistborn, one Elantris, one Warbreaker and 7 Dragonsteel. That makes a minimum of 24 years. Does Sanderson have an ETA? I'm not in a great hurry, but I'd really love to see it finished before I kick the bucket. I don't wanna think how many people following various long running series passed away while waiting for their story to end, and it'd be nice if I didn't join them.