Jan's comment:

I agree.

In fact, you mention of course but a few of the alternative scenarios possible. As soon as one drops the idea of the classroom, even as a metaphor, a guise in which it is, for instance, still very prominently present in online learning settings and other forms of distance education, then there is hardly a limit to the number of alternative spaces, situations, and modalities one can imagine in which one learns.

I am not sure, though, if the simple elimination of the idea of the classroom would as such alter out conceptions and pre-conceptions about learning, though I recognize that it might help.
Some tough thinking is required to rid ourselves of such ideas as that learning ought always to result in an increase in one's store of explicit knowledge or our abilities to perform particular well-defined actions at a particular level of competence. Important aspects of what one can become, such as a wiser person, have little to do with these changes. Yet, learning, in a way different than normally defined, is important for becoming wise. The fact that wisdom occurs, and often prominently so, among people whom we call illiterate, shows that important aspects of learning have neither to do with the classroom, nor with the processes that normally happen in the classroom.

I guess that the reality is that the classroom is not and never was 'the main site for learning.' The problem is rather that the classroom has become overvalued in the minds of most people as a site for learning and that therefore we do no longer see learning when it happens elsewhere.