Should there be a comma before "though" when it occurs at the end of a sentence?
Solution 1:
Though is used as an adverb in this case, applied to the verb is, therefore no comma is strictly necessary.
Saying this, I can easily imagine a brief pauses between is and though when speaking the sentence, hence a vocative comma is acceptable.
In other words, take your pick. If I can avoid a comma (as in this case), I usually will. It's not wrong either way though.
Solution 2:
I'd use the comma, but modern style would probably omit it. There is a general tendency towards less punctuation. Look at Victorian novels, and then compare with modern prose - there is much less punctuation now. Or look at the King James Bible; that is rife with colons and semi-colons that would not appear nowadays, often not even 'demoted' to commas. Punctuation style has changed over time.
Solution 3:
I strongly prefer the second form, with the comma.
Say out loud, without a pause
I don't know how outdated it is-though
Nonsense-speak to me.
Solution 4:
I believe both are correct. In general, you would use the comma if you would pause at that point if you spoke it aloud.