Honestly, why? Considering the rather insane amount of time something like jekyll needs, a few seconds don't matter at all. So having a background service won't really get you anything for "production" usage – even if you'd be doing twitter-like 20+ items/day micro-blogging. The only gain I could imagine from a setup like this would be prototyping the look and feel of your site in its very early stage, where it would save you from half a dozen script invocations.
Those seconds would only matter if they would be a large percentage of the whole running time. And I've yet to see a SSG where two, three seconds for a year or more worth of blogging would actually matter.