I'm only on late 2018 shardcast, but I'm 100% current on all Cosmere works. Now before I get into my inaugural hairbrain theory, I want to establish a few things that we already know or seem to know.
Part 1:
1. Vessels can somewhat guide the shard based on personality.
2. A being can hold multiple shards at once.
3. The shard can potentially re-coalesce.
That means:
Essentially, for someone/something with unlimited patience, it could be possible to quietly wait for a while while a shard coagulates into something claimable.
Part 2
Kelsier has been Preserved for a long long time. He's essentially stuck. And if he hasn't figured out how to leave, I think he has plenty of time to do so.
Spren can be summoned across the cognitive realm to other planets, meaning something deeply connected to a certain planet can potentially leave.
Part 3
Todium happened. Nightblade is super OP and can yeet a vessel straight into the spiritual realm.
Theory:
I've long held that Kelsier is the ultimate villain of the Cosmere. Given all of the upheaval and eventual shenanigans that will occur over SA5 and MB Era3, I think Kelsier will end up holding the power of Odium. But, with him as the vessel, it's not the same Odium. We know that Rayse was a turd, and his personality emphasized certain characteristics of the shard. When Kelsier picks it up, it truly becomes passion. That same violent "kill all the nobles" passion that we've seen before.
And because he's had so much longer to wander the Cosmere, and with his expanded consciousness, he has determined when and where the shattered shards will coalesce. Within a very short time, he will pick up Ambition to become Lust. Then Devotion And Dominion to become Zealotry. Within a very short time, we now have a Vessel holding 4 of the most dangerous shards.
With a quarter of the Shards possessed by one vessel, the Cosmere is in for some crazy rough times.
Kel, of course, is going to think that he can exert his personality and use the Shards for good. But we all know how that'll turn out.
