In my opinion extending the s57 to Journal Square is not a good idea. I honestly cannot see that benefiting many Staten Islanders and a closed door route would exacerbate the traffic on the Boulevard.
Having a few 10's start and end on Staten Island on Richmond Ave/Forest & Morningstar would be ideal.
Thinking about it some more from a previous post, my proposal would not degrade service. The 10 would not have to bypass its southern terminus at 1st & JFK, it could make that stop, make a right turn on 1st, a right turn on Avenue A and access the bridge from there.
As you may recall, my suggestion would be one stop on Staten Island where riders can transfer to many popular cross-Island routes.
Additionally, I think its worth discussing the roles HBLR & existing local buses which serve two completely different ridership demographics:
a) HBLR is, partially a way to connect Hudson County to each other, but particularly Downtown Jersey City as that area is a hub for most private businesses (finance, technology, retail) and as a way to revitalize downtown Jersey City.
B) Most buses in Hudson County begin/end at Journal Square because that area is the municipal (and formerly a major commercial hub before downtown) for residents of Jersey City and the county. The justice complex (Superior Court, Municipal Court) is located on Newark Avenue and Summit Ave respectively, Hudson Community College. Also, given the buses (10) route through residential areas I think it would link more folks with transportation options than the HBLR
I think extending the 10 would be the best idea because again it would benefit more people.