Well, that’s what I’m hoping will eventually happen.
But to clarify, I think it may be unwise (and unfair) to boast LTS support from the start. Being honest, those who truly need LTS level stability probably aren’t (yet) your appropriate target market. Such users should be encouraged to stick with 16.04 to see whether “Ubuntu Unity” pans out, or else encouraged to move to a flavor with a longer track record. Rather, your target market, at least initially, should be those who are a bit more adventurous.
So better to take a wait-and-see approach initially. You can always extend support later, if appropriate to do so.
But if you absolutely will never do both, then I vote for only the 9 month release cycle. And I do so for selfish reasons: I use the 9 month release cycle.