There is certainly interest in more scramble races, and as you know from BBR7, scramble races do suit the fighter class ships pretty well.
I suppose the simplest way to judge a combat build would be to say that all weapon mounts must be fitted with weapons (of the same class as the mount, so no putting small weapons on large mounts), the ship must have shields, and it must have sufficient power to operate all of those. A regulation ship could also be interesting - possibly the only time we might be likely to have a regulation Viper build
I kinda like the idea of a regulation build, possibly as one of two classes (an Unlimited class with rules like you mentioned, and a Formula Viper class, say).
I think it might be fun to encourage... forcible deterrence of interdictors by having a category for largest bounty collected during a completed run, too.
Initial thoughts on rules...
1). All weapon mounts must be filled with appropriate class.
2). All utility mounts must be filled
3). Power distributor must be largest possible class
4). Shield generator must be equipped and shields must be operable (i.e. it has to be able to handle the ship's mass.)
5).Must have enough power to run all systems except cargo hatch/fuel scoop/fsd/interdictor if you have one with hardpoints deployed, and enough power to run everything but the cargo hatch with hardpoints retracted.
Anything I'm leaving out?
I'd like to tune it so that it's possible for a Viper or an Eagle or a Fer-de-Lance to seriously contend if well flown.
EDIT: Thinking about it, the last scramble race was won by a Viper, and I'd guess a Viper is very good bet in this one. Also, a combat kit Viper is actually a little expensive for a newbie if one wanted to enter. Therefore I suggest the regulation class should be the Iron Eagle class. Flying the standard Eagle Mk. II, of course, not the Imperial variety (which I think is another very good bet in Unlimited if the jumps are short enough).