Should see-through head-mounted displays be also used for completely immersive (non see-through) applications? Technically, it's certainly possible. Just put a dark cover on the front glass, and you have something similar to being completely immersive. However, having the extra weight, the not-quite-as-bright image and a bulkier product is certainly a downside for dual-use HMDs.
This reminds me of the washing machine / dryer combination. What a great idea on paper - no need to move laundry from one to the other. In practice, there are so many drawbacks to this combined approach that most everyone still has separate washers and dryers.
Not to showcase my age too much, but as a teenager I owned an Apple II computer. Not an Apple IIc. Not an Apple IIe. A real Apple II (serial number had 4 digits) and at that time, it would connect to our standard TV through a small conversion box. But, even though it made sense at the time, computers migrated very quickly to separating the TV from the computer monitor. Same concept, different time.
So... I still think see-through HMDs and fully-immersive HMDs should be kept separate for now.