This is a very important question that a lot of people don't seem to be aware of, and can potentially save thousands in taxes if they have children in daycare. There is very little information regarding the DCFSA change for 2021 and is difficult to find answers for these questions. I'm in the same boat where my employer will not adopt the increased limit.
I'm fairly sure that the Household limit is $10,500 regardless of one or two spouse, so it wouldn't be an issue if you spouse can opt in to their work contribution for $5k. The problem is that this won't fall under qualified "Life Event" changes, and it would have to be approved by company HR, so it depends on how flexible your HR is on qualified changes.
An Audit is unlikely in this scenario and even if there was, you would just explain about your understanding of the new limit. Even the IRS website doesn't say anything about this, only that the household limit is increased to $10,500.
