That depends if they have a crystal ball to know if WotC will not sue them until they have no money or will to pay for lawyers like TSR did in the good all days. Remember, Hasbro (like any big company with an IP portfolio) has on their payroll lawyers happy to sue anybody since that is proof they are needed at the company. On the other side you have small companies like GR that either asked a close friend or had to pay a lawyer just to make sure they undestood fully the GSL. With such posibilities looming on the horizon the will to support a new game system with suplements grows quite dim I would say.
Dude, read the copyright laws. They are far from being this big iron monkey with which to crush people who try to publish stuff. If it was you wouldn't have had Judges Guild and others. They were not shut down by lawsuits.
In fact, copyright law has become much more clearly defined in the last 20 years and is a safer path then ever to walk. All you have to do is make sure to keep your path clear fo pitfalls, and that is far from hard to do.
Copyright protects you from blatant copying/plageurism, that is it. Stay away from blatantly copying what WOTC prints, stay away from their trademarked and copyrighted terms, and your safe.
ITs pretty simple to go the copyright route. As long as your capable of being smart about it.
Copyright is far from being iron clad protection. It is pretty weak when you think about it. Except in the case of out right copying someones work. That is the only time it really protects you.
To make it clear, copyright only really protects someone from having their work copied, word for word. Change the presentation, change the layout, change the look of the charts and graphs you use, change XP charts numerical progression, and your good to go.
The 4E "SYSTEM" is not protected by copyright, despite several people on this board claiming otherwise. US Copyright law very clearly states that systems, mechanics, etc... are "In no case..." protected by copyright.
The copyright WOTC has for "D20 System" are for those words only, not the system itself.
Don't believe me? Go to the US Copyright application website and use their search function to look up WOTC's copyrighted stuff. No system is copyrighted. Only words are.
The copyright route is nothing to be feared, just travel the route carefully.