BioWare has been deceptively vague about where the next Mass Effect is going, with fans not sure whether to call it Mass Effect 4, or Andromeda 2, or a completely new title entirely. One major implication that players have been clinging to, however, is that the next game may see the two Mass Effect galaxies coming together in some way.
While building some sort of connection between Andromeda and the Milky Way might have some larger implications for the Mass Effect series as a whole, it may mean more for the protagonists of each game. Specifically, players may get the chance to see their own Commander Shepard meet their Pathfinder Ryder, which could open up for a whole new way for BioWare to tell its stories.
Pro: Keep Both Series Relevant
One thing that players had to come to grips with when first playing Mass Effect: Andromeda is that the new title would be a complete departure from the characters, and even the entire galaxy that they had grown familiar with. On the other end of this lack of familiarity, the new series introduced new alien races from Andromeda who now have their own lore and backstory that is full of mysteries to uncover. So, bringing Andromeda and the Milky Way together could manage to keep what players are already familiar with relevant from both the original series and the more recent game.
Most importantly, players may be able to see the effects of their decisions play out on a massive timeline thanks to the 600-years of travel that Ryder and the characters from Mass Effect: Andromeda have experienced. Considering that the impact of three games worth of decisions was one of Mass Effect 3's major criticisms, showing some of this impact continuing down generations can make up for those earlier complaints. Similarly, the state that players left the Milky Way in during the original trilogy could lead directly into how much assistance comes to finish uncovering the secrets of Andromeda.
Con: Ryder in Shepard's Shadow
Unfortunately, bringing these two worlds together and having Ryder meet Shepard could leave the new character even further in the shadow of the legendary protagonist. So, having Commander Shepard return in Mass Effect could have the side effect of making Ryder feel unimportant in comparison to the literal savior of the galaxy. This was already a hump that players had to get over at the start of Mass Effect: Andromeda, becoming familiar with a whole new character who feels like a clone of the previous protagonist.
It's a natural part of how BioWare crafts characters, allowing players to make them as serious, mean, or sarcastic as they want, that can make all of the protagonists feel incredibly similar. This even happens to a degree with the Dragon Age heroes, with the Gray Warden, Champion of Kirkwall, and the Inquisitor all feeling like the same character depending on how the player controls them. So, bringing Ryder and Shepard together could really highlight the problem between Mass Effect's protagonists in a way that may be better addressed in gameplay than in dialogue.
Pro: More Choices Between Both Protagonists
One of the major draws to BioWare titles as a whole is the massive amounts of roleplaying options for players to both choose who comes along for any missions, as well as who to fight or help. Having Ryder and Shepard meet could also mean that the game will be split between the two protagonists going on separate missions and mixing and matching their party members among a shared pool of characters. This could even work with Shepard's morality system from Mass Effect, letting players have one renegade and one paragon protagonist that might butt heads if they're alignments diverge.
Having two protagonists to choose from can also give the option to decide to take whichever is the player's favorite to the most difficult missions in Mass Effect, while leaving the other to handle easier adventures. It isn't likely that the player will be able to switch between the two on the fly, but having two characters to choose from could also give certain missions new ways to be approached by shifting between the two in the middle of a firefight. Though, while having the option to have these two characters exist at the same time could open up for unique gameplay opportunities, there are quite a few difficulties to overcome.
Con: 600-Years of Separation
The major indication from the latest Mass Effect trailer that the next title will be bringing the original trilogy back into Andromeda's storyline is the inclusion of Liara T'soni. While the Asari could have survived for the 600 years it took Ryder and crew to reach Andromeda, Shepard couldn't possibly live long enough for the opposing protagonist to come out of stasis. So, bridging the 600-year gap between Ryder and Shepard's storylines would mean having to find a way to make sure that the protagonist who theoretically sacrificed themselves for the fate of the galaxy shows up half a millennia later.
There are a number of ways that this can be addressed, though many of them would imply making one of the three Mass Effect 3 endings canon. Granted, that alone might be disappointing on its own, with the sacrifice that the player made at the end of the original trilogy being overwritten, as well as the choices being irrelevant. The other end of this would be that Shepard has died before, so bringing the character back specifically to meet Ryder wouldn't actually be out of the question for the series. This is a sci-fi franchise, after all.
Pro: Build-Your-Own Romance
Bringing Ryder and Shepard together in the next Mass Effect could also give players a chance to be more hands-on with one of the series' most beloved features. Specifically, giving players the option to romance Ryder and Shepard together could mean creating both characters to be one part surrogate and one part romantic interest. This could even give players an added incentive to revisit the series in the Mass Effect: Legendary Edition, in order to shape the romantic paring to take whatever form they want.
This would naturally mean ignoring the perfect companions that some players already chose, like Garrus from the original trilogy, or Peebee from Andromeda. However, this could ironically give one of the best options for a human romantic companion, given that Mass Effect's alien races tend to be much more interesting.
A new Mass Effect is currently in development by BioWare.