Manufacturers may decide to solder the SSD directly to the motherboard, like Apple currently does with RAM on their laptop computers. This is beneficial to the manufacturer because it's more compact, less chance of mechanical failure, easier to assemble (pick&place instead of humans), lower price etc. In short: it's very attractive for manufacturers.
For consumers this is worrying though, as with the RAM on Apple laptops:
- You cannot replace a failed SSD, you need to replace the entire motherboard
- You cannot upgrade the SSD, so you have to accept the ridiculous price stepup when ordering the laptop (i.e. the 200 dollar price bump to get 8GB extra RAM on a macbook pro)
- Laptop is less valuable when trying to sell it on after a couple of years, because the storage size will be low compared to new SSD's.