Okay, we will assume for a moment that the next game will be a continuation of the first two - as wikipedia puts it, in their article on the Sith:
The Old Sith Wars... And for a moment we will assume what some people have speculated - that there is a force in the outer rim, (possibly in the mysterious Cloak of the Sith region), that still represents Sith power, and Revan and Exlie are going to take it on...
If this is the case, it might be cool to have a different structure from the two previous games - a generic small first level, perhaps again on a ship - followed by the usual choices as the charecter searches for evidence - followed this time by more than one end levels arranged in a linear format - in that case I would like to see the following:
Choice levels when searching for evidence, or the location that Revan has gone to: Coruscant
Alderaan
Mon Calamari
Duro Orbital Cities
Korriban A made up planet, perhaps based on India or something, maybe one of the Republic
'Ord' planets...
Sullust maybe
Ziost maybe
Kessel might be a cool gangster world, but then it might be worth making up an older Republic version of a spice planet, like Manaan provided a different drug from Bacta
And a couple more... maybe
Yavin 4 cos of the Sith connection...
-Coruscant would provide a nice starting planet, as the investiagtion into the destination of Revan and what is out there could be set on the fantastic metropolis itself, and could depict the reforming of the Jedi order following the Civil War - it would be the generic megacity setting, and has lots of potential.
-Alderann, or perhaps Naboo, could fill the role of the generic garden planet, and many people im sure would like to be able to explore Alderaan, as it is an important planet in the Star Wars setting.
-Mon Calamari would provide a familar yet new destination full of Mon Calamari and Quarren charecters, and would be the generic water planet type setting.
-Duro would be very interesting, as Duros are along with humans perhaps the most common and widespread species in the Star Wars universe, and were probably founding members of the Old Republic. Since their population is living in cities above the polluted planet, it would make for ideal space station type levels, but also fill in some much needed background on such an important species.
-Korriban is required, because it will always be so important to the Sith, and because it fits with the theory of what the plot might be like so well. Id like to see a different area of the enigmatic planet this time though.
-Sullust might be cool as an all-underground planet
-Ziost would be cool to see, but might not be neccesary
Planets I wouldnt want to see:
Manaan - one visit was enough
Onderon - same reason, not that interesting
Dxun - same reason, no point going to ones we have already seen when we could be seeing new ones
Malachor - same reason, also it was boring at the end of KOTORII
Nar Shaddarr - great planet but its been in about 3 games already
Dantooine - no point going back there, might as well meet the Jedi order on another planet, i.e. Coruscant
Kyshyyk - been there
Bespin - not sure it exists yet, and if it does, we are already familiar
Corellia - same as many other generic planets, Alderaan or Naboo would better fullfill a garden planet and Coruscant would better fullfill a city setting
Hoth - there is nothing there
Mustafar/Geonosis/Daghobar/etc - no point putting planets in just because they have appeared in the films, Mustafar for example is a minor planet, and Daghobar would be pretty boring
Ossus - is irrediated
Definatly not Endor - Ewoks are annoying and meaningless, no point going there when they were only made important by the fact that the Death Star was in orbit, and no point picking every film planet when the galaxy is meant to be full of tens of thousands of inhabited planets, and more abandoned ones.....
I think the planets in KOTOR 3 should be from other games and the movies. 
Coruscant
Linear Mode
