'Decentralization' without fully-validating nodes is not really decentralization. Each node in a decentralized network must be able to verify all transactions for itself.

Accordingly, the only nodes that count for decentralization are those that maintain not only the transaction forkbranch of the data, but also the witness forkbranch of the data.

The sum of the transaction forkbranch of the data, plus the witness forkbranch of the data, is somewhat larger than it would be if the witness data stayed in the same block. There is additional data needed to correlate the correct block of transaction data with the correct block of witness data.

For a fully validating node, the resource demands are accordingly higher for The SegWit Omnibus Changeset than a simple bump of maxblocksize.

That is only the first layer of how The SegWit omnibus Changeset is bloating bitcoin.

It is smaller than franky1's scenario, but it does not require his/her (fully rational, BTW) interpretation of Core and Blockstream statements of what they might want to do in the future.

edit: overloaded use of fork replaced with branch