I think wallpaper would be great in your entryway. My only word of caution would be to think about what you would use as a “finish” at the end of the wall that contains the front door. If you paper only the facing wall and the wall to the left (as you enter the front door) that problem won’t exist.

Oops! I see now that you would also need a “finish” at one end of the wall facing your front door. But if you can solve one corner edge, you can solve the other.

Not the best set up for wallpaper, specially with the change in ceiling height on the left side.

I wonder whether a decorative paint technique (roller, stamp, stencil) would be more practical, while producing an effect similar to wallpaper.

Wallpaper is tricky there. I have a similar situation. Although i adore wallpaper , in the past i have used decorative painting techniques on the entry wall, and the base color on the adjoining walls .

Wallpaper is great in the right entry. I don't think this is the right one. Yes, you can find ways to end it so it can potentially be doable. But that doesn't mean it is the best area for such an application. I don't think this space calls for it. A larger more interesting rug would be great.