The 3E SRD has been used clone and/or create 0,1,2,3,3.75 edition along with dozens of non D&D rules, there is nothing stopping someone publishing game material that is 5e compatable, as long as you avoid trade dress etc. FGG just first to do it. I imagine there will be a lot of errors in the products, but not enough to make them bad. Matt Finch or Skeeter Green mentioned on the kick starter that the lawyers have checked the legal stuff, so they are not going into it blind like the SRD5 site
I AM NOT A LAWYER, but I have published a product that used the OGL. I do not believe the above is correct.
Here is what I believe is the case:
D&D 3.x was published under the OGL. It constrained anyone making 3.x-compatible products.
D&D 4.x deliberately avoided the OGL, which meant third-parties were not free to make compatible products, and doing so could be a violation if IP. Doing so would put you in a legally questionable position.
Other companies, writing game products for non-OGL games, could and did use the license voluntarily in order to secure a particular place in the market.
The license does not grant IP to WOTC, but it does ensure that any derivative projects must also use the license. The OGL is, as far as I can tell, a genius invention that can continue to be used by companies who either are creating materials that derive from OGL stuff, or are wanting to have others build on their work, and have it also under the OGL. In our case, it was both.
Possibly the 4.x products that have been mentioned fall into that latter category, or perhaps there is something else afoot. In any case, to my knowledge 5.x is not OGL, and there have been no official announcements for unrestricted third-party materials. We know they've hired other companies to produce adventures; I would be hesitant to do anything that potentially infringed on 5th, because I can't hire lawyers who can beat their lawyers.
I hope this helps.
