Frotz supports zblorb and gblorb files. I do plan to add other backend interpreters, starting with TADS, then probably ADRIFT. I've had a couple of people requests Level 9 and Magnetic Scrolls as well.
There are portable interpreter libraries targeting glk already, so this shouldn't be too hard, except for the major complication of auto-save, which is required to be viable on iOS but no terps have facilities for out of the box.