There are two problems I see with negotiating the next block chain:
which transactions to include in the chain (because consider transaction T which has propagated through exactly 49% of the network at the time the next block is negotiated)
which proposed block to consider the next legitimate block in the chain, because even assuming all nodes have all transactions, what's to stop every node from attempting to propose the next block, thus forcing the network to attempt to propagate and resolve N different block collisions.
In bitcoin, number 2 above is easily resolved by intentionally imposing conditions on the resulting hash of the blockchain such that it is computationally difficult to derive the hash, and thus collisions (where 2 nodes propose a valid block/hash at the same time) are very rare.
Outside of bitcoin, I'm skeptical as to how new blocks are announced and agreed upon. If you have a blockchain structure where a new block should be announced at an artificial time interval of every 10 minutes (assume the network is time sync'd) then what's to stop all your nodes from attempting to propose many different next blocks all at once? In a general blockchain network that isn't bitcoin, I don't see any restriction like #2 above that reduces the ability for many nodes to come up with their own proposed blocks and to stop them from trying to announce these blocks to the network.
Also, assuming we can resolve this issue ^ and manage to negotiate which block to use as the next one in the chain, we're assuming here that the contents of all the proposed blocks are also equal. How can a network negotiate the next block if 49% of nodes contain a transaction that the other 51% of nodes do not?