You can't just up the notoriety cap.
Once you master a weapon, you stop gaining rep with it. So if you up the overall notoriety cap without upping the weapon skill cap, eventually you'd hit the point where you couldn't gain rep and your progress would stop, except for quests. I don't think you'd make it very far past 40. So you'd also need to upgrade the weapon skill cap.
If you upgrade the weapon skill cap, things start to unravel. You need to add more skills to use up the skill points you get. I think there are enough open attack, skill, and passive slots to give every weapon two or three new ones, but I think there's a limit of 8 skill, 5 attack, and 5 passive skills. It would probably not be trivial to expand that, especially the skills, since you'd have to redo parts of the UI to add a 9 and 0 skill.
Or you could just allow people to fill up their existing skill slots, but I really like that you have to decide where you want to put your skills. It adds variety.
Or maybe get around that by introducing new weapons, but I think there's a hard limit of 6 weapons in the game engine. It's fairly trivial to add new types of weapons in the existing slots, but a new slot is something else. Again, this means changes to the UI, plus new animations and models.
Or allow more than 5 skill points to be allocated in each skill. This would probably take the least work, but the power increase on the weapons has its own problems.
So now you've got your uber-buffed level 75 pirate, with skill 50 in all weapons, and every weapon skill has 8 points in it.
What are you going to kill? You go to Tormenta and hit Sweep, and all the Urchinfists drop dead. But what'd be the point? They're all grey, and you get 0 rep.
And now we come to the real problem. There would need to be high-level content. And there's a lack of that now.
It would have to be some pretty serious stuff to give your uber-pirate a challenge, too. Something like a level 80
this or
this (with hulls made of PURE AWESOME).
And that would probably mean some new and
more powerful ship types for you to stand up to them. I'm drooling on my keyboard just thinking about it.
And new islands and zones with really high-level mobs in them.
So it's not just a notoriety cap. Changing that changes the game balance, and that's really tricky to get right.