Bose hasn't announced plans for a carrying case or slip cover for the T4S or T8S.
The hard cover for the T4S and T8S protects all the ports on the back. Only the headphone jack on the side is exposed. The T1® cover left all the ports exposed and the cloth cover helped with that.
I've seen people toss their T1®s into a bag along with cables and microphones and bits and pieces of hardware. I cringed to see it but I never saw any significant damage as a result.
I like the design of the T1® cover, but the T4S/T8S cover is a one-piece design. There's no moving parts to break. Although I've never broken one of those covers, I know others who have.
I'm using a large SLR camera bag from another life for the T8S and microphones.
You can't see it in the pictures, but there are generous pockets on the ends and an expandable section on the back that holds the ToneMatch power supply and several cables.
I've been using this as a gig bag since the early 90s. It's indestructible.