It's been shown that you can publish stuff for 5e without a new 5e OGL. There's a kickstarter for a new monster book right now from Kobold Press and I just backed the Primeval Thule 5e kickstarter. So, yes, it can be done. Heck, on the front page news of this site, they're talking about EnSider's 40th article. It's not a secret. You can publish for 5e without an agreement with WOTC.
The best advice- consult a lawyer. That's the bar as it stands right now. If you want to publish for 5e, go see a lawyer first and make sure that you're not violating any copyright laws. IOW, the only bar is money.