Don't Wait If You Find Something You Love
While the OnePlus 7 (and the Pro) have the potential to be a very exciting phones, we don't know too much yet. You also must consider that while it'll have big changes, it'll still be considered "incremental" in terms of what's new. There's only so much you can do with a phone.
Basically, if you find a phone that's amazing right now, something you love, don't wait. Instead, buy a phone now and enjoy it. Maybe you love the stock Android and amazing speakers of the Pixel 3 XL, or see something great in the OnePlus 6T or even a new phone from Oppo or Xiaomi. There are several amazing phones, and one might be enough to get you on board. Especially the beautiful Galaxy S10e.
Basically, we're fairly confident the OnePlus 7 will be worth the wait, but that's all we can say at the moment. So if a good phone or deal comes around, and you're up for it, go ahead and snag it.