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The two or three remaining parties (that aren't narrowly self-selecting based on education or work-field like the above) are all focused on Taiwan or the Kuomintang legacy. The Revolutionary Kuomintang is some kind of left splinter group of the KMT. (By the way, unlike in larger NPC, they are afforded most [non-CCP] seats in the CPPCC--a consultative body, but on par with CDL.) The Zhi Gong party is also historically related to ex-KMT warlords [and thereafter was based in Hong Kong]. The Taiwan Democratic Self-Government League is supposedly representing [some] Taiwanese [descendants].

And one might think that the Chinese Peasants' and Workers' Democratic Party would have a broad[er] appeal and membership given their name that they trace their history back to the 1920s. But nowadays they seem to function as a medical association. And if Wikipedia's description is possibly in doubt, the official news about them also stresses that

CPWDP has played a full role in in-depth research, particularly in the medical services, population and ecological environment fields.

On par with CDL as number of seats is the CNDCA (China National Democratic Construction Association), which seems to be more like an interest group for entrepreneurs in real estate & construction. I'd also describe this as self-limiting in its appeal.