Seagate has been doing that for years now.
their approaches are very different.
seagate has 8GB ssd to act as a fast super cache for the stored data. the firmware intelligently studies your usage and will cache frequently used data to ssd
wd has mutually exclusive ssd and hdd partitions. we can install windows on ssd and keep data on hdd for example. but you'll need special driver /software to enable the hdd partitions. I don't like it.