Obviously if the factory offers it, then it's possible. One way you can get a pretty good idea of whether a current system supports multiple drives is to look at the configuration options available from the factory. Some laptops that have a WWAN slot (mobile broadband) can accept an mSATA SSD installed there instead if you don't want WWAN, but that's not true of every system with a WWAN slot, and information about which models can accept mSATA in their WWAN slot unfortunately isn't readily available. As you've noticed, some can have drives installed into their optical media bays, others have a mixture of SATA and mSATA/M.2 connectors, and still others just have multiple M.2 connectors. And even among the systems that support dual drives, the connectors are different. SOME current Dell systems support dual hard drives (some support even more), but definitely not all of them.
