Then we're back to my earlier point. There is no 'value of education' bubble analogous to a housing bubble. An individual's degree isn't tradable in the same way as a house is, so the value of that individual's degree isn't being bid up by people competing to buy it. So what would it mean for the bubble to burst?

If you're talking about a mechanism by which the price of newly-issued degrees were to fall (i.e. college tuition sticker prices fall by 50% within a year or two) then, even if it were to happen, that's just a fall in the price of a consumer good. If the price of laptop computers falls because people realise they can do their work with tablets and chromebooks, we don't think of that as a laptop bubble. Not a perfect analogy but I hope you get my general point: if you're calling something a bubble, then you've got to be able to point to the stock of existing assets whose price is out of whack with fundamental value (e.g. based on future cash flows) due to irrational investors bidding up the price.

I'm not claiming tuition fees are in line with fundamental value to the recipient. If they're not, then it's just people buying stuff they shouldn't. If they are in line, but it's for signalling reasons rather than the education received, then there's economic inefficiency due to market failure, but it' seems still not a bubble.