Landing on the taxiway is often not unreasonable from the ground perspective, provided a few precautions are taken.
The taxiway bearing strength is either the same or stronger than the runway (assuming that the parallel taxiway is open to all the aircraft that can use the runway and is not some light aircraft special). No strength problem there.
The taxiway surface has less texture and will certainly be ungrooved, so that high speed (>50 knots) in wet weather could present friction and aquaplaning problems.
The structural width is less than the runway, which means that crosswind can be a problem. Taxiway structural width is probably 23m, and for the larger jets (ICAO code 3C and upwards) there is usually a low strength 6-10m wide sealed shoulder on each side to reduce erosion and FOD. If the shoulder is there, then reverse thrust shouldn't be a problem. It would be a rare case that it isn't, but the worry then would be that the outer engines would be hanging out over the grass.
The other concern is crosswind and operations on reduced widths. That's discussed here:
http://www.pprune.org/forums/showthr...hreadid=114235
BTW – I vaguely recollect that at Gatwick, the parallel taxiway was designed to be used as a runway during closure of the proper runway. Very clever thinking. Avoids the unseemly rush of major runway repairs or overlays and work at night, and allows the job to be done right. I'm sure the guys at Cape Town wish they had had the same luxury. Not that I'm suggesting they rushed the job during the 6 hours they allowed for the work at night. Not the first time, nor when they redid the first time's overlay a year later
