That's a good question. There was my line of reasonning :
1_ I just coded something close to what i'm doing in java (using spring), and that made me feel to stay as far as i could from that bloated ecosystem (although the language in itself is ok)
2_ I looked at golang but was scared away when i saw that there wasn't generics or anything that would code some "meta level" functions. Plus, it still felt not broadly enough adopted at that time. Yet it IS the language i'm planning to rebuild my project for now (although i'll probably first rebuild just a small part of my api to see how the language behave with business process modeling and DB interactions, because i'm still very skeptical).
3_ I love C# , frankly the best language hands down, yet i don't like the idea of depending on the MS ecosystem (i've always felt like one day they'll come and make me pay big time). Plus windows seems like a falling platform to me.
4_ I just coded a moderately big website on django, and a big "sudoko-like" generator in pure python and loved the expressiveness and power of that language (as long as you're using the default data structures). Speed never was an issue, and since it was basically just a website, reading the django documentation was everything i needed. I had a look at ruby but frankly there wasn't a big enough difference to make me want to switch.
i know some people (the european southern observatory here in santiago) that use zope interfaces to address your concerns. i find the whole idea somewhat odd, but they seem to like it and make decent software, from what i've seen.
+1 The zope component architecture properly used is a thing of beauty. To see it in practice, probably the best example is the pyramid web framework. Most of the important things in pyramid are expressed in terms of interfaces and components so if you want to use your own you just plug it in. You've got a much higher chance of it working in pyramid than (for example - not in particular) django.
