Definately needs a new section. As already mentioned the Punto Evo which is essentially a facelift of the Grande Punto has a seperate section and whilst the Punto Mk1, Mk2 & Mk2B are all in one section, they should really be seperate. That's kinda in the past now though & as Mk1 numbers are dying down it'll become essentially a Mk2 section.
However, with a model that's likely to have strong sales and therefore a strong presence on the forum (unlike, say the new Doblo) and that's (as a minimum) got all-new exterior panels, new interior, new or tweaked engines and modified steering & suspension system, it would be totally out of line with the GP & Punto Evo if the new Panda were not to have a new section.
I think labelling the sections simply with the years of production would suffice, ie Panda 2003-2012 (or Panda 2003 onwards if it remains in production for now) and Panda 2012 onwards, plus the usual small photo should be ample for people to distinguish between sections. You'll still get the odd person that posts in the wrong section but some people can never be helped no matter how much labelling there is.