I would not replace a complete ERP (or any other) system with a blockchain version of it. 99% of the functionality would not fit to the abilities of blockchains.

But I can think of a relative simple way to achieve "trust" in any system where data should not be allowed to be changed.

• The ERP or whatever system stays like it is (using RDBMS as data storage for example)
• It need to be defined which data need to be immutable (not all data inside such big systems need to be immutable, so not necessary to track it for everything)
• Each data record which should be immutable will get hashed (included a timestamp) automatically by a new function within the ERP system when such a record get saved
• The generated hash will be stored in any public blockchain
• From that point on a controlling instance can verify that every saved record in the system do have a hash and that the hash is also saved in a separate blockchain (with timestamp) and that those two hashes matches.
• If someone try to change any data in the ERP system, this would generate a new hash which is not available in the blockchain

With this method you could prove that every recorded transaction in the ERP system was never changed after creation.

I'm quite sure there are some flaws within this simple idea which need to be looked at, but from the basic concept it would work.