ah i love the Roci and i think that this could actually be a decent ship for us to provide, cheap patrol cutter meant for inter system police or convoy escort and as a picket ship in larger formations. change out the pdc cannons for light laser cannons and ion cannons with the missile system being anything you could load (so proton torpedoes, anti star fighter, anti missile, connor nets, ect) and you'd have a very good cheap ship that we could crank out in numbers.
also Advent while yes it hasn't been invented yet, and i know how strict you like to be with cannon, this is a quest. if it is offered or allowed in the future i would love for the Neb-B to be a ship we make, why, because it was a effective ship used by a lot of people so we know it would sell. and also remember this is fanfiction we can do anything we want with the story if the OP allows.
Edit: also as you pointed out it hasnt been made yet and since it was introduced at the tail end of the clone wars it is likely that it isn't even in the design phase yet so it is technically nobody's yet to make since as you pointed out it is still years off from being made and used. also since this is a Ship Design Quest id assume that there is going to be a lot of theft of future cannon ship designs and out of universe ships sooooooo yeah, just gonna say that id imagine once this gets rolling that people are going to be lifting and stealing ship designs left right and center so just saying that we cant make something because it is made by a different company a couple of decades from now or isnt from this universe is silly to me.