Nico wrote: <<What do native speakers of such a language think?>>
I have actually faced this question back when I did my novelisation attempts in Finnish. I always had all the crew members (only series 1-2 crews, mind you) using the familiar "sinä" instead the formal plural "te" when talking to each other. Only Zen and Orac were exceptions here (Orac seems to have the knack of sounding matter-of-fact and up-yours-mate at the same time), so in my mind Avon would definitely say "Oletko sinä pettänyt minut?" Actually, since contemporary colloquial Finnish frequently eliminates the pronoun altogether (because of brevity, redundancy and probably a need to evade direct address), he might say "Oletko pettänyt minut?" Then again, that kills the dramatic emphasis.
Bear in mind that the use of formal address (we call it "teitittely") is not nearly as common or strict as in German, for example; if you aspire to be a primary school teacher in Finland, don't expect the pupils to address you with "te"; suggesting such a thing will just get you laughed out of the classroom. Its use has become more and more vague and infrequent over the last ten years, a phenomenon which the more conservative language watch dogs usually attribute to the degenerative influence of English. So having one of the crew members use a formal address when speaking to another would suggest the existence of an explicit hierarchical system which I don't see there at all. Outside of Travis and other military personnel addressing Servalan with "te", I also had Blake address Sarkoff and the Stott formally, not as a gesture of subservience but merely as an acknowledgement of an older person's stature in a situation where you don't actually know him but need his trust badly. Never Travis, though: there is no suggestion of either seniority, respect or a need to adhere to any social code that would prompt Blake to use a formal address. Vila might do it in "Hostage".
Since I've got the excuse to talk about translating, the thing I always found much harder was finding the right register for the dialogue. Blake's 7's dialogue is certainly tight and snappy yet it can also be very contrived and theatrical, not very vernacular. Looking back on my translations, they tend to be overly stiff and formal (even taking into account my linguistic skills at the time), and with Vila one always gets the feeling he should sound more colloquial than he does. The difference between written and spoken Finnish can be very wide, and while you can trasnscribe the formal features of spoken Finnish into writing pretty well, it's not very clear when you should do that. It may also be the dialogue's tendency towards the kind of neutral sci-fi dialect, where temporal tell-tale signs like contemporary slang or pronounced regional accents are downplayed to homogenise the language and also to make it sound more "timeless". This would suggest a rather formal tone throughout, one that is neither too pretentious nor too obviously vernacular. But then perhaps I'm reading this all wrong.
Kai