Doctor Futurity
Hero
Actually it would be more like creating a video game that works on the PS3 without Sonys permission or license, and THAT you cannot do. Analogy's with video games get mixed up though since they are completely different beasts.
They key variable here is that the OGL lets you do a lot, up to and including create modules that use or refer to the same open content features identified in the OGL while modifying the numbers to conform to 5th edition standards. I can't think of any good analogies, but its definitely closer to the dominion of open source engines than anything else if you want a computer game comparison.
The OGL was a crazy Pandora's box and they knew it. The question now is whether WotC wants to let the flow of 3PP be directed by the old OGL or if they'd like to take the reins again and produce an updated version which lets them have a direct say in contemporary products aimed at 5th edition compatibility. That way at least they can protect current IP and also immortalize this edition of the game in much the same way 3rd edition ended up being the focal point of the last 14 years of RPG design.