yeah, you are an old bear :) Blocktrades was the opinion 1MB is doable, only hivemind would maybe make some problems.
But I'm sure it would not be impossible to fix.
And if a Block is not at 100%, it would be less than 1MB:) it is only the maximum :D I would expect it would need much more users and transactions to fill 1MB.
Edit: even 10TB is not that much if we think really about it. It is on today's data streams close to nothing.
I know replay and start a new witness note after some years could be maximum pain, but I remember 1GB hard drives and less. And its not that long ago :)