these "words" are actually representing the "entropy" that is used to generate the individual private keys. so unless you can come up with a way to generate the same level of security entropy (at least 128-bits) using 3 words, it won't work.
The idea is, people just need to memorise 3 words + passphrase (of their choice) (strong password) rather than worrying that the (seed phrase 12 or 24 words) is stolen or lost. Any reason why this cannot be practical or recommended?
are you really suggesting that memorizing 3 words + something like
J\{m^"<Aw2ATdn)V96
is easier than memorizing this:
legal winner thank year wave sausage worth useful legal winner thank yellow
i'm not convinced!