...or he's just bored with the various employment he's had over the years and looking to something that superficially interests him. Machine Learning from the outside seems like a fun field to get into (whether it is or is not on the practical side) so that's where he wants to turn his attention.
I'm sorry but a lot of your generalizations only apply to someone living in a certain box of life. 15 years of experience "approaching paying off your mortgage"... are you kidding me? Sure for some people but that's certainly not the average. Even with more people getting 15 year mortgages 15 years out of school doesn't necessarily put you into the position to be at the end of that and those first few years you weren't necessarily making that kind of cash anyway. Add in things like Student loan payments, car payments, family, eating and well maybe even living your life outside of the office and being at the end of your mortgage term is SO not to be expected at this point.
Failed engineer? Maybe but certainly not clearly from his description. The only dig I would say is with a MS in CS and 15 years in the field I would think he would have figured out how to explore new technologies by now without asking /. As for not being able to quit his day job: I like to tell my friends I live paycheck to paycheck on *really large paychecks. That's my choice. I like to live every minute of my life outside of work to the fullest and that costs money ergo I'm not banking it away. I've managed to survive a couple employment hiccups just fine and so like living on that edge. He might have a family to feed (I don't) or huge student loans (remember the MS) or etc etc etc that are burning away those paychecks before they can be saved. Kudos to you for being extremely frugal with your money but most of the population require their paychecks to continue, even those of us with really large ones.
Anyway... I must've really felt like typing today (or avoiding that pesky day job of mine) since trolls don't typically deserve this kind of bandwidth. Thanks for providing some much needed distraction!
As for the OP's questions:
1) It might be... go try it! Google is your friend and will lead you to things like Coursera or Open Source projects or Amazon's Machine Learning tools or or or..
2) Contributing to Open Source projects is your best bet for practical experience in the field OR taking a hit to get an entryish level job in the field and proving your worth inside to get back to your 15 year salary expectations. Honestly if you've got a solid resume and that MS of yours getting a job shouldn't be the hard part.