As Snipe says, leafnode will have exactly the same problem as newslink,
which is that your BBS callers will most all their articles, including
spam, as you. This could get you in trouble with your provider.
I have been working on a solution that'll allow your users to
authenticate with my usenet server with their BBS credentials and
anything posted will be under their account. Nightfox is currently
working on a usenet client for Synchronet so you won't have to feed
selected groups into your BBS but it'll just act like any other news
client, it'll download x number of headers and thread them and only
download the body if called by the reader.
It will also allow people to use a regular nntp client to connect to
read news if they choose to do so. I'm working on populating a new
server right now, but it's taking a lot longer than I expected.