Warning! The following contains spoilers for The Flash episode "The Speed Of Thought." Read at your own risk!
Even though The Flash had only just said goodbye to pretty much every other Wells that ever lived, it wasn't the end for Tom Cavanagh. Sure enough, Cavanagh returned in the latest episode in a role we're all familiar with, but also one we know next to nothing about. It can basically change everything, provided the return of the original Harrison Wells is legit.
An ending scene replayed the Season 1 moment where Eobard Thawne arrived at the original Harrison Wells' car accident to steal his identity. After Thawne made his transformation, we then saw a new sequence in which the evil speedster dug a hole for Harrison Wells' body and dumped the brilliant scientist inside of it. The camera stayed on the grave, which slowly began to have green sparkles form above it. Those sparkles turned into a person, who seemingly was the original Harrison Wells resurrected.
If the original Harrison Wells is back from the dead, this is huge. Keep in mind Eobard Thawne took on Wells' identity in 2000, so everything that happened after was Reverse-Flash in disguise. All of Wells' landmark achievements, his hiring of Cisco and Caitlin, and his relationship with Barry Allen were actually the work of Reverse-Flash. This Wells doesn't know anything about Team Flash, why they're in his lab, or what they're up to.
One interesting thing to note is that Thawne's plan to create The Flash was based on the original Harrison Wells' creation of The Flash. Before Thawne traveled back in time to toy with his arch-enemy, the original timeline (according to the Season 1 episode "Tricksters") had Harrison Wells developing the particle accelerator in 2020 and becoming someone connected to The Flash. It stands to reason Harrison Wells could replicate the particle accelerator correctly and perhaps correct Barry's speed and the Speed Force.
Of course, there are some key parts to this whole mystery that are missing. The Flash didn't reveal exactly how much time had passed from Harrison Wells' death to his alleged resurrection. If it was shortly after Thawne departed, then there's a huge question of where Wells has been this whole time and why he didn't return to S.T.A.R. Labs to reclaim his life. If this resurrection happened post-Crisis, obviously, it's a bit more understandable why fans haven't seen him.
Well, there's kind of a twist there, too, like always when it comes to Wells. It's not like necessarily the real Harrison Wells, I guess. It has more to do with the particles that made up all of the Wellses now embodies this Harrison Wells. So, we're going to yet again see Tom do something slightly different than we've ever seen, and it is technically the real Harrison Wells but with a twist.
It seems that the Harrison Wells resurrection took place in the present, sometime shortly after Barry destroyed the artificial Speed Force after his speed thoughts ruined everything. The Flash fans may remember that the device was powered by the multiversal particles of all living Wells, so it stands to reason they escaped when Barry damaged it. Much like with Nash Wells, they need an organism to exist in, and they just so happened to find the perfect one lying in an unmarked grave. This would mean the original Harrison Wells is alive and possibly living with the knowledge of all other Wells.
That'd be handy for Team Flash, though I can't even begin to imagine what the show has planned for Tom Cavanagh after. That seems to be what Grant Gustin was getting at in his quote, but it's just a guess and The Flash could have something completely different planned. It's hard to deny, though, that having a Wells around for this crucial moment in Season 7 would be handy, provided that teased twist doesn't make him evil or something.