Well, we will be gaining access to essentially like beta 3, correct? So that means we have to be gaining access within the next 2 or so weeks... Kinda disappointed... I was expecting the public beta to come alongside the developer beta 3, so yeah.
I don't know what you mean by essentially like beta 3. But everyone who gets access will receive an email directing them to the page that gives you the beta profile installer. Once installed you do the update OTA. My guess is people who already had 8.3 and 8.4 access can skip the installing the profile (since they should already have it enabled on their device) and find the update through OTA. (You won't get a prompt, you have to go into software update manually to see if the update is there.)
But then again iOS 9 might use/require a new profile as I don't know if the current one is iOS 9 and OS X Yosemite specific.