How about this:
All gismu which do not share their first four letters with an official gismu are hereby reserved as nonce-gismu.
They have no inherent meaning, but may be given one with cei and are used in the manner of the broda series. Thus, you can keep using pitsa to mean a pizza, but you must say something to explain the vague idea of pizza first, then append cei pitsa onto it. One can use salsa to mean salsa, but to do so first clarify it with a sentence using some other brivla - probably sasno - with cei salsa. You get the idea.
-mi'e. kreig.daniyl.
Yes, but! What if one person uses "xogro" experimentally, and another person uses "kogro" experimentally? These aren't blocked by any standard gisnu; but they do block each other, so one has to win — which one? Whichever one is being used in that particular conversation. cei-bound words lose their meaning when you say co'o and go chat with someone else.
Of course, non-standard gicmu are non-standard, so making prescriptions about them is kinda silly, but I would like to see the community adopt some subset of Type 4 fu'ivla for this purpose. We have already blocked off CCV'VCV for cultural pseudo-gismu.