yes yes yes, glass please!!
portals are beautiful- the animation and all; not just useful but also decorative, they make place look better;
and if you frame it like this:
just imagine how better it might look with glass blocks looking better; you create pictures that are alive, I already imagine a space dedicated to portals (and after the limit of 3 being close removed) - 10, 12 and more portals framed, put behind glass, creating a gallery of living pictures - new art has been born
you still leave the other side free to enter, only one side gets glass and is made for viewing only; the portal above looks like this on the use side: