Somehow I missed this thread until now. I'm currently in my first year of an ID MFA program without a design undergrad degree, so some of my observations might be helpful.
The program I'm in currently has 3 grad students coming from non-design disciplines. I think this is kind of weird because the program itself is very traditional. I was admitted in the interaction design focus, presumably because my visual skills aren't great. The IXD curriculum is the same as ID though, with 5 classes subbed out. Before being accepted into grad school, I took sophomore level courses in design sketching and CAD.
I have two weeks left in my first semester, and have some reflections:
It would have been better to get an undergrad in ID. Even with the groundwork in design that I did, It's hard to be competitive in projects. I could liken it to trying to write a book in german after taking only one semester of german class. Sure, you could do it, but your output isn't going to be great, which makes you wonder why you tried in the first place. Unfortunately for me, my financial/work situation prohibits me from doing an ID BA. I also felt like it would be dumb to get a third undergrad degree.. Which I now think is wrong. I am finding that in design, it's not about the piece of paper, it's about the portfolio. If you can find an instructor to help you learn, forego school entirely and just practice until you can make a good portfolio.
Also, figure out what you intend to do with design. Over the last semester it's really hit me hard that what I have been wanting to do all along isn't as much Industrial design, as it is some form of system design, or some role tangential to ID. I like thinking more than drawing. lol. I'm still trying to figure it out. The program I'm in is straight up product design. Most of the ideas I have are of little interest to the faculty. I'm now far enough along, that I'm going to try to finish the program, but in doing so, I'm going to have a portfolio full of things that have nothing to do with the jobs I'll be looking for.
I guess my overall recommendation to other folks looking to break into design from another background would be to start at the start. I think jumping in at the masters level is just a waste of your time. (unless you find a program that is designed to train you on the business or marketing of design or something) You'll understand design better, but I don't think that will really help your career.