how sure are we that we are indeed getting DP Remakes today?
There's nothing to really put a number on it, but let's break it down this way. Masuda and Ohmori are both pushing this hard on their social media, which they don't usually do, which mildly suggests it's a core title (which they'd be involved with) and not a side title (which they would not be).
I think Galar has had its moment for now (suggesting it's not more Sword/Shield DLC) and I think it's *way* too early for Generation IX, so if we assume it is a core title, Sinnoh is next in line for "traditional" remakes, where Johto would be next if they continue the new line of games begun with LGP/E. These being the two most plausible (not "likely," just plausible) options, it's not a coincidence that these are what the rumors focus on, because the rumormongers who subsist on clicks and views know they have a 50/50 chance of being right and they can write it off even if wrong.
"Leaks," "rumors," "fan requests," whatever, all just noise, none of it credible, and all of it better left ignored. There's always chances it could be a different core title or not a core title at all. But if we look at what we know and what we don't know but is plausible, it leads us here.