In conclusion, after analyzing around 214 million domain names for CAA records, the following are worth noting:
1) CAA records are still not widely used.
Across all TLDs, only 1.4% of domains use CAA records; out of the Top 1M Domains, only 4.8%.
Considering that CAA records have been around since 2010 and honoring them has been mandatory for CAs since 2017, this seems like a pretty poor adoption rate.
2) Most people don't set 'iodef'.
Those domains that do use CAA records tend to use the 'issue' and 'issuewild' records, but only minuscule fraction (0.9% of all TLDs' domains; 3.2% of the Top 1M Domains) set 'iodef'.