I would argue that any subtopic that requires more than basic understanding of the parent topic is too specialized for a general knowledge encyclopedia.
If you mean general knowledge in the sense of "knowledge which is generally held," or even "knowledge which is generally accessible," then a general knowledge encyclopedia wouldn't be that useful, by definition, to most people.
Crucially, it would be useless to the people most likely to use an encyclopedia!
A general knowledge encyclopedia should aim to curate knowledge with no discrimination in terms of category. This is what Wikipedia is, and it's really good at it.
I think there is room for improvement in linking topics and subtopics, even potentially in-line within an article. See a word you don't understand? Click the "+" next to it to expand a sentence that fills its place syntactically and semantically!
[1] https://en.wikipedia.org/w/index.php?title=Special:Preferenc...
proof of concept of something like what you're describing: http://www.telescopictext.org/text/pFjkqQY9bmfvQ (not the best example, but telescopictext is very cool)