The likely rationale is that there's probably quite a few people who want the deployability of PHP without having to work around the problems with the language.
I don't see any practical reason to translate Ruby to PHP. Compared to other translations, this one doesn't make sense at all as you don't get any advantages of the translations result.
Compare this to a translator that translates Ruby to JS: Here you get the ability to run Ruby in the browsers. Or JRuby where you get the ability to run Ruby in a Java-only environment (plus a bit of performance in some cases), or IronRuby for the same reasons for the .NET platform.
But PHP? I don't get it.
So unless your time is really cheap ($2/month, that's, considering a 40 hours week $0.0125/hour), you'd be better off just getting a rails hoster.
No. This feels like it's of pure academical value.