There are several problems with this. Firstly, a machine-readable validity ruleset would basically just have to be a library implementing the rules, simply because of their complexity - for example, one of the previous validity changes requires scripts of a particular format to be treated as hashes of the actual script, which is provided by the transaction redeeming it. Secondly, bugs in implementations can effectively cause the to enforce unexpected additional rules, such as the BDB lock limit which caused an unplanned hard fork a few years back. Thirdly, everyone involved still needs to be a skilled developer with knowledge of distributed systems - especially the currency steering committee, since changes to the validity ruleset can break the whole thing in subtle and unexpected ways - and the committee still needs in-depth knowledge of the actual implementations to know if they can cope with their planned rule changes.