first of all there is no active code in the software which can deal with Steem on the steem.dao account (Proposal System). Only with SBD. Secondly nobody can access the account. And yes most likely in future hard forks proposals will be written exactly like you say, about destroying it (simply sending to null). Undoubtly those will be written and have a high chance (if you ask me) of getting honoured.

This is actually being put in the hands of the voters through the Proposal System, so you can have your say what should happen with it.