delericho
Legend
If I were to release this, I wouldn't be doing so for money. It's quite clearly a derivative work - making money from it would require a proper commercial license.
As I understand it, you don't need to (intend to) make money from something for it to be copyright infringement.
The third-party products thus far have released using the OGL, and have made sure to stick within the bounds of what can be derived from the existing (3e) SRDs (plus, presumably, references to plain-text rules terms like 'advantage' and 'challenge'). But you should really consult a professional before going down that route. (In general, though, I suspect the OGL-ish route is your best bet if you want to play it 'safe'. Thus far, I haven't seen any indications that WotC are going to oppose such efforts - though that might just be because they've not noticed yet.)
Fair Use for most part allows you to do things like, "Compatible with D&D ™ 5th Edition", so there's no need for what some people do ("Compatible with the 5th edition of your favorite fantasy game").
While this is true, as I understand it one of the terms of the OGL is specifically that you don't make specific claims of compatibility. So while in general you can do as you say, you can't if you're using the OGL - by using the license you agree not to do so.
But it's a very long time since I looked at that, so I might be mis-remembering - could be the d20 license that did that.