You need to find a better interwebs.
Us regulars here with a decent track record of predictions have been saying no update to the 12.9 iPP this year (especially considering that a 256GB model was introduced in March of this year).
Having said that, if you've waited this long, I suggest waiting a bit longer until October's event just to be safe. THEN (I honestly don't expect any updates to the 12.9 iPP) keep a sharp eye out for sales on the 12.9 iPP at places like Staples and Best Buy. (My bet is that Staples will have another $150 off deal)
Any deal that offers $150 off or more on the 12.9 iPP after the October event... take it. But be warned, there will be those who will claim that there will be better deals on Black Friday. You might be tempted to wait for that. Historically, that has NOT happened. Then around Black Friday time there will be more rumors of how there might be a December announcement (some claimed that last year) and/or that a significant upgrade is coming in March 2017.
But if you are the type of person who will be kicking themselves if an update is released within 6-8 months of a purchase then wait... wait... until 12.9 iPad Pro 2 is released and then jump on that at the time... don't wait after that.
The current 12.9 iPad Pro is a beast of a device. I've been using mine every day for the past 6 months and there is nothing that Apple could announce for an update that would cause me to regret my purchase. But that's me. I'm odd that way.