Of his "Thesaurus," Roget said: "I am fully aware of its numerous deficiencies and imperfections, and of its falling far short of the degree of excellence that might be attained."

so, just what could be done to improve upon it?

Ooh, ooh! Cross-reference it with the OED? Failing that, I need to know something first: how big is the real thing? More than one volume? I ask because I strongly suspect the one I have is an abbreviated version.