Customizing news.arc to your liking shouldn't be too challenging if you're willing to program in Arc. Neither should writing your own application similar to news.arc using a web framework for one of those languages, e.g. Ruby on Rails. However, trying to use news.arc and somehow mix it in with your Ruby and PHP code would be a lot trickier, IMO.
To be honest, I am completely new to Arc and news.arc.
I thought building a Hacker-News like forum with news.arc would be faster, but maybe I should be focusing on what I know and build with the languages that I actually know.
Is it possible to reverse-engineer? news.arc, because I will probably have a bumpy ride to program "ranking algorithm" like the one used in news.arc (Hacker News).
Hacker News's ranking algorithm isn't public, is it?
At least, it probably isn't in our version of news.arc. As Paul Graham says at http://arclanguage.org/item?id=12468, "I should release a new version though. News.arc is greatly improved since the last release." (I assume the ranking algorithm wouldn't escape scrutiny....)
I noticed that a few pieces of the algorithm were not released, and the algorithm has surely changed since arc3.1, but the published code explains at least the overall behavior of Hacker News ranking.