I was thinking the {tlhIngan maH; taHjaj}, and I don't think that it captures adequately the intended "feeling" of the original "remain klingon".

The english "remain klingon", doesn't express a wish; it doesn't mean to say "may we remain klingon". It is an imperative.

The sentence is in the imperative mood, but it is clearly an expression of a desired state. Here's another example:

Buy or die!

In English, these are two imperatives. But Klingon is happy to ignore the imperative and present this as a conditional:

bIje'be'chugh vaj bIHegh

Klingon does not have a grammatical subjunctive of the hypothetical, so it uses conditionals combined with indicative mood. If it did, if there were a verb suffix -foo that meant hypothetical subjunctive, then you could say bIje'be'chugh vaj bIHeghfoo, and it would work perfectly.

And that's what you've got with tlhIngan maH; taHjaj: an imperative in English becomes a subjunctive in Klingon. -jaj produces a subjunctive mood with a wish or may meaning.

Why not translate this as an imperative? Why not translate Buy or die as an imperative? Stylistic choice, most likely. There's no reason why the phrase couldn't have been yIje' pagh yIHegh; we know you can conjoin imperatives like this. I find Qov's tlhIngan maH; taHjaj more suitable to a slogan than any of your suggestions, purely on the basis of sounding good.

All this goes to show that translating concepts and sounds may be more important in some contexts than reproducing grammatical features like mood.

-- 
SuStel
http://trimboli.name