This is according to this post on Reddit in which it shows an alleged email conversation between user midnight_watch and Valve’s co-founder Gabe Newell. According to the email, it seems that the Steam Deck will use a socketed M.2 2230 SSD, suggesting that maybe if users wanted, they could swap it out for a cheaper and faster third-party alternative, or have it fixed if anything goes wrong with it.
However, the email does mention that while it does use the M.2 2230 SSD, it wasn’t intended to be user replaceable, meaning that Valve probably does not encourage users to tinker around with it and swap it out, even though technically you can. This is kind of like third-party mods like we’ve seen for the Nintendo Switch Joy-Cons, where users can swap out the casings for it even though it’s not officially supported.
That being said, we shouldn’t get too excited yet. While it could be physically replaceable, there could be other hurdles like software that could prevent that from taking place, but it’s still interesting to note the possibilities nonetheless.