If there was an easy way for non-crytpo users to get tether, then it could be a potential substitute for SBD. The problem though is that this is only available for a very small percentage of 'apt' users, and the people we are trying to onboard would not be able to benefit from it.
Technically tether is not guaranteed to "always equal to one dollar" either. It has it's own pegging mechanism, akin to SBD, although it (currently) does a better job at holding it's peg than SBD.