In a <gallery mode="slideshow"> it would be very helpful if we could optionally display the thumbnail bar by default.
Currently, it requires a user to click on the middle "toggle thumbnails" icon for the strip of images to appear beneath the first image.

Having this option would help readers to see:

• how many images are in the slideshow (roughly from a visual glance)
• which images are distinctive in some way (e.g. perhaps a gallery includes 5 photos and 1 illustration)
• if any new images have been added since they last looked
• that a slideshow exists (if they missed the arrow controls)

The instance I noticed this at, was https://meta.wikimedia.org/wiki/WMDE_Technical_Wishes/Show_text_changes_when_moving_text_chunks where a 7th very distinct image was recently added. I wouldn't have noticed it, if I hadn't methodically/randomly gone through the 6 images which I've already seen months ago.