"I think the only reason this isn't likely is that we've already had a series that ended with someone becoming God. So, while what you propose is certainly possible in regards to the rules of the cosmere, it doesn't seem likely from a story-telling standpoint. It could quickly become, "Oh, look. Brandon Sanderson wrote another book about somebody becoming God. ZZZZZZZZZ." So, in summary: Possible? Yes. Probable? No."
Technically, all his shardworld projects involve people becoming gods (The Elantrians, The Returned, the one in Mistborn, and I think he stated that at Writing Excuses).