Use the diald package. This is on sunsite in the same directory as the PPP source, /pub/Linux/system/Network/serial.
There are no plans to put filtering into the PPP code. The 1.3 kernel supports a firewall option and you should use that rather than attempt to find a method of putting firewall logic into a network device driver. Use either the ipfw or ipfwadm programs to define the rules for the firewall code in the kernel.
It is in the 2.2.0e package.
There is a netbios PPP protocol. However, your better solution would be to use TCP/IP and the \samba\ code.
Microsoft and others have used Netbios PPP protocol.
The nbfcp protocol is a public document and available from several sources. The Netbios protocol is not a valid address family at the present time for Linux. Until Linux supports the protocol, there is little need to support Netbios over PPP for Linux.
ISDN support revolves around having a working ISDN driver. The present design of the PPP driver does not lend itself well to the concept of a block of data being received. This is being changed. A driver for the Sonix interface is being developed.
Multi-point would be nice. I am not aware of anyone working on multi-point support at the present time.
There are small changes needed to support a serial interface which uses synchronous communications. The redesign of the PPP driver will help with this function as well. Kate Marika Alhola has expressed an interest in writing such a synchronous driver for her hardware. You should contact her at kate@iti.fi or kate@nic.funet.fi for further information.
She informs me that the current status of sync ppp is, that I have had it few months in \production\ use talking with Cisco(TM) in speeds 64K and 256K. The source is under the GPL license and it may be found in ftp://nic.funet.fi/pub/Linux/kernel/xnet-sync-driver-1.0.tar.gz.