Has the hardware actually changed? Apart from the Rotax which wasn't around back then.
The fibreglass technology is pretty old.
The low weight has been achieved by cutting corners everywhere, from the safe business of stripping out all possible sound/thermal insulation, to the more dubious practice of very flimsy control linkages. A lot of the ultralights are "hang glider construction" standard, with a cockpit to keep the bulk of the rain out.
To get down to say 750kg, you don't get something for nothing. Short of building every bit of the whole ship out of carbon/kevlar (which would make it cost £200k+) .