Also, does OGL cover 5E? I thought with the new release that they would be able to go after any blatant copies of their system.
As I understand it, you could in theory clone 5E without even using the OGL. Copyright does not protect game mechanics, only the expression of those mechanics. As long as you're careful about not copying any of the actual
text of the PHB--rewrite everything in your own words--you should be good*.
In practice, of course, you'd be walking a dangerous line. If you slip up, you're screwed. Even if you don't slip up, you'd better be prepared to defend yourself in court, and whether you win or lose, that ain't cheap.
However, the core of 5E is very, very similar to 3E, and virtually all 5E terminology can also be found in the 3E rules--in most cases, with the same or very similar meaning attached. What you could do is create an OGL bestiary and class book--create your own versions of monsters and classes, designing them to be compatible with 5E rules without actually duplicating those rules. That would be inarguably covered by OGL. Then anybody could create adventures based off your material. It would not be a clone, exactly, but it would enable the production of third-party 5E material under OGL terms.
You could even make your material cross-compatible with Pathfinder. Maybe things are going to be different in the final version of 5E, but going off the public playtest, I'm fairly certain that would be doable (in contrast to 4E, which was rather sharply incompatible with previous editions).
[SIZE=-2]*Although it's worth watching the outcome of Wizards's lawsuit against Hex Entertainment. Hex is producing an online CCG which is pretty blatantly Magic: The Gathering with the serial numbers filed off. Same turn structure, same card types (different names but same functions), same pretty much everything. There's no OGL involved on the Magic side, so this lawsuit goes straight to the heart of the question: Can Wizards, in fact, prosecute you for copying their mechanics if you don't copy their expression of them? It will probably end up getting settled quietly out of court, but if it does go before a judge, we'll get some clarification on the law.[/SIZE]