I'm told that when using a server-side resource pack, the minecraft client will have a name of "Server" and that only one RP is ever added to the list.  AFAIK, this appears to be a limitation of server usage of resource packs and client use (players manually adding them) directly.  I don't know if there is an API that should/could use the filename itself (which is what appears for players), so that more than one RP could be added to the list?  As it is, due to the name, any attempt to add another will overwrite the one already present with the same name and then the player loses the previous one.  

Can more than one be defined in the server.properties or via a Plugin like ForceResourcePacks to push it up to the client?  Alternatively an API to change the name to match the filename so that more than one can be added to the stack of RPs?

The only choice a server owner has is to combine ResourcePacks into one so that the player can have both.  However, this violates EULA with the owners of the RPs.  Any insight into a solution would be greatly appreciated even if it isn't a bug for Spigot to fix.  Having the API to use would be very helpful to support multiple named resource packs.   Thanks - Steve