Poser Debut is entirely affordable at the base end of the market?

There's possibly scope for SM to update aspects of that, if this was something that was strategically desireable to them, from a marketing perspective, to get people into using a new batch of SM sponsored content... I would guess.

It wouldn't surprise me too much if that happened at some point not too far off, after any new figures that rely on weight mapping coming out from SM.

Technically, I'm guessing that a new version of Debut would probably be a feature-constrained version of Poser 9;

e.g. with the ability to load and pose content, but no manipulation tools, etc.

So, anyone serious about their 3d art will likely still want to save up and graduate to Poser 9 or Pro 2012...

...then save up even more and get Zbrush, so they can use the forthcoming new GoZ feature in Poser Pro