These restrictions could have been implemented in past, but with current size of playerbase, it would just make people suffer.
I mean, if you restrict trading factions only to trading ships, they will stay defenceless. Hiring escort or calling lawfuls for help often won´t work, because there is not enough players to provide this. In past, when you shouted in emergency skype channel for help, at least 5-10 people immediately logged. These days sometimes even no one come. In past, there were almost constantly military/police players in every house, but that is long time gone.
It would just force people to make chars from more factions. Now if corporation player needs help, he calls in his own faction channel first and some other member can come with his faction escort ship. Result of restriction would be only that mentioned player would log local lawful indie char created for the same purpose. Players would simply go around this restriction anyway, they are doing it already even now.
Regarding cargo - it would make trading even boring. Being stuck with few types of cargo (and thus just few routes) will only make traders bored even more quickly than it happens now. I would have no problem if every faction would have some "special commodity" which could be hauled only by them, but wider restrictions would not bring anything good.
