I think a simple definition of a "bubble" is when (irrationally) high demand pushes the price for something above it's actual value.
So, I suppose it could be fairly said that higher education could be a bubble if the price of tuition (and 4 years lost wages) is unreasonably high compared to benefits the BS/BA degree bring.
If people then realized this and chose not to attend universites to such an extent that we had enrollment declines we could see that bubble burst. Overall declining enrollment would represent a decreased demand and force universities into financial problems.
I earned my degree decades ago, tutition was relatively inexpensive compared to today and my starting salary was quite high for that time even though we were in a pretty big recession. So I consider my money well spent. But I'll add that it wasn't an easy degree, probably only 25% or less that started in the program made all the way through.
Howver, the kind of of money non-degreed tradesmen and the like charge has become quite high. HVAC techs, plumbers, electricians etc in my area charge per hour as much as many professionals (lawyers and CPA's).
I have seen more non-degreed people making more money than educated professions etc for some time now. If can you manage a crew, whether in contruction or cable installation etc you can make more money than just about anybody else (excepting of course Wall Street types and senior execs at large companies).
Another 'little secret' is that those with heavy equipment make heavy $'s. Start out with cheap an old used bulldozer or backhoe and keep adding on equip and soon you'll find all kinds of contracts open to you. Most people just don't realize the kind of money these people make. There are more redneck millionaires than you can shake a stick at (I find it amusing about how people now claim there is no upward mobility etc in the USA and all the ranting about how the top 2% keep making more and more $).
If and when younger people figure this out enrollment should drop at regular universities. JUCO's have all the basic courses (biz mgmt, accounting, economics, marketing, finance etc) any tradesmen wanting to start their own business would need. Then there are trade schools to focus in on the actual work you intend to do. Spending thousands of $'s and 4 years sitting around in classes you don't care about and won't use isn't the way to make big bucks. Why would it be? Anybody can do that.
Fern