The question is absolutely not "can more than 2mb can be uploaded?" The question is not, is it possible to run a node? The question is, at what point do bandwidth limitations disincentivize the operation of full nodes
The answer to that is 'at any block size whatsoever, including as little as one transaction per 10 minutes'. There is absolutely no realizable direct positive incentive for any other then a miner, merchant, or exchange to operate a node. None. There is no renumeration for so doing. None. Nada. Bupkis.
to the extent that centralization endangers security and fungibility?
That canard has no place in a 'core vs classic' comparison. Fact is, any fully validating core node with the SegWit Omnibus Changeset implemented will need the signatures in order to validate. The fact that they have been repartitioned into a separate chain means nothing to such a node -
it still needs the signatures in order to validate. Accordingly, The SegWit Omnibus Changeset is as big a disincentive to operating a node than is classic.
But it's really kind of irrelevant - as has been pointed out, an insignificant proportion of current nodes will stop node-ing simply because the disk space required goes up from $3.09 worth to $6.18 worth, nor if they need to go from 10 MB upload every 10 min to 20 MB upload every 10 minutes.
But it is still really kind of irrelevant - the dirty little secret is that independent nodes essentially fulfill zero marginal utility. Sure, every node validates transactions. Guess what - so does every intelligent miner. They would not risk building a block that has a transaction included that would be rejected by the rest of the network.
Summary:
1) 'Node Centralization' is no reason to choose between 1MB Core and 2MB other
2) Doubling block size will have negligible impact upon node count
3) In the end, nodes are negligible marginal utility anyhow.