Blockchains makes sense as a distributed ledger where each party doesn't trust the other too much. Note the words "distributed" and "trust". That's why it was developed to make Bitcoin work. Outside of "DeFi" - cryptocurrencies - they were never found really useful. Whenever the blockchain approach has been used in a centralized system, it was soon clear that there are faster and cheaper approaches to obtain the same. After all, banks have been transferring money for centuries without.
Now, if Reuters and Canon can get AP, Magnum, Sony, Nikon, NYT, Le Figaro, CNN, BBC etc. on the same boat, and build a blockchain where any change to an image is recorded into a distributed system not controlled by a single entity, a blockchain could make sense. A blockchain run by Reuters itself only doesn't make any sense. Anyway, one of the problems of a real distributed blockhain is the time it requires to approve a transaction. So, it is feasible probably to record everytime an image is "published" to the blockchain. Blockchains also don't play well with large data, so storing whole RAW/TIFF images into a blockchain won't work very well. C2PA is designed to store a thumbnail of the images inside is data - it is enough to identify all image changes properly?