Japan¡¯s Topix stock benchmark climbed to a three-decade high on Monday, drawing even more attention to its future amid plans for a sweeping market reform.

The Tokyo Stock Exchange is set to undergo a once-in-a-generation shakeup in little over a year. Japan Exchange Group Inc., which owns the bourse, plans to cut the number of market segments, apply new listing criteria and turn five confusing, overlapping divisions into three simpler sections: blue-chips, startups and the rest.

A key goal seemed to have been to overhaul the Topix, whose membership has almost doubled since the 1990s to over 2,000 companies and includes more than half of Japan¡¯s listed firms, into a much slimmer benchmark of top-performing, well-governed firms. But some are already voicing concern that the changes may not result in the dramatic transformation that had been hoped for.