According to Wikipedia the expected date for completion for the OED revision process is 2037, which revision “is expected to double the overall length of the text.” (Of course, as with the Forth Bridge, it’ll then be time to start the work all over again!)
There’s an apt passage in Tristram Shandy in which our hero muses on the task of writing his Life & Opinions:
I am this month one whole year older than I was this time twelve-month; and having got, as you perceive, almost into the middle of the fourth volume–and no farther than to my first day’s day–‘tis demonstrative that I have three hundred and sixty-four more days to write just now, than when I first set out; so that instead of advancing, as a common writer, in my work with what I have been doing at it–on the contrary, I am just thrown so many volumes back–was every day of my life to be as busy as this–And why not?–and the transactions and opinions of it to take up as much description–And for what reason should they be cut short? at this rate I should just live 364 times faster than I should write–It must follow, an’ please your worships, that the more I write, the more I shall have to write–and consequently, the more your worships read, the more your worships will have to read (IV, xiii, 228).
Hmm, 24 years. I’ll be a feisty 88 by then. (There’s confidence for you.)