CMcC Advocacy for tcl is a fine thing, widespread tcl popularity would undoubtedly bring considerable benefits, but I think it's worth considering the benefits which currently accrue to tcl because its usage is not as widespread as (say) PERL or PHP's.
That's not to say I think we should stop trying to popularise it, merely that we should occasionally reflect on what sort of popularity we'd choose.
== The long tail ==
One thing that widespread popularity inevitably brings is a long tail of out of date users who absolutely refuse to upgrade, but do want just that one bug fixed. This tail can slow the evolution of a language through effort expended backporting bugfixes.
== Committees ==
We love to hate the idiocy of some of the W3C recommendations, but to some extent they are an inevitable consequence of popularity. Once a thing is popular, and people/corporations have spent real effort/money using it, they acquire an interest in distorting future development to maximise their ROI.
== Negative Normative Standards ==
Related to both the preceding points: imagine if you had to pull out an API book everytime you wanted to use tcl or tk. Tcl has a minimum of language lawyering, but as applications in tcl became more popular, the interfaces between them would tend to become more like DMZs, no-man's-lands littered with historical decisions (aka 'mistakes'.)
== Slowvolution ==
The dragging tail of backward compatibility, the byzantine operations of committees, the battlegrounds of negative normative standardisation all tend to slow evolution.
== Summary ==
Popularity has merit, but it may be that we've dodged a bullet in not attaining world stardom.