Thank you Chagrin and Crossroads....
Littlebits... Yes! There is a connection. (They had a credit in the page of which my post speaks before I read Chagrin's post!)
JeeLabs boards... yes, I see what you mean... but wonder if the JeeLabs boards are really the place to put novices? And whether they are the least expensive option for schools, where "class sets" are needed, and budgets tight.
I wouldn't claim that my ideas are particularly original or wonderful... what I was hoping for feedback on was whether they were SOUND?? Does my scheme protect the Arduino, do you think? What could a user do... if they didn't "mess with" the pinMode statements... that would result in permanent damage to the Arduino or a component?
(And, a secondary question: Would the system be too limiting? Yes- the loss of flexibility as to whether a pin is used as input or output is a drawback, and no, you couldn't connect, say, an Ethernet shield... but if you accept this is for INTRODUCTORY activities, can you see day-wreckers in my ideas? (As I said... there are ideas in the wings about providing power to modules.))
Re- my "credits" to the other initiatives, above, in more detail...
Littlebits: It has been many years that I have been trying to find a "safe" (from pupils!) Arduino for schools. It was in fact a conversation with a teacher friend who wants to do some Arduino stuff with high school kids, and who was wondering if maybe Littlebits was the answer, that put those questions to the front of my mind agian. I would be DELIGHTED if Littlebits is the answer... but I haven't yet been able to satisfy myself that it does. I've had some information from them. If I am reading correctly what I've been sent so far, their system doesn't offer any more protection to the Arduino than mine does... and maybe less. But replacing the Arduino part in their system is rather more expensive that replacing the equivalent in mine. I'm also a little nervous about how good the electrical connections between their modules are going to be, and I just generally dislike "closed" product lines, unless they have a USP I really, really want access to.
Jeelabs: Some nice modules, and the interconnect question addressed... but again, expense is an issue for me. Do I really need to pay the "extra"? And tie myself to one supplier?
I'm sure they both have a place in the marketplace... the Jeelabs success-to-date makes it pretty clear that others feel the same way. I am surprized at the lack of "chat" about Littlebits... looks a lot of fun, and just the sort of product that a tax-payer-funded school might well buy in. The lack of chat is a little worrying, if I am going to tell my friend that Littlebits looks good. Sorry Littlebits... I wish your venture well... but don't want to be one of the pioneers, this time.