I would also be very interested in Rebels if they moved to hard plastic, especially if they took that opportunity to add in additional heads for alien races on the sprues. Doesn't feel quite as Star Wars only having the occasional alien dotted around, at that point I worry they just look like generic fatigue wearing army men.
I use this table to determine which models are hard plastic, I've been trying to exclusively collect that particular material as I have no interest in the soft plastic.
The only thing on this table I feel is incorrect is the Priority Supplies Battlefield Expansion, while the parts are not on sprues but instead in individual bags they are the same plastic as the vehicles.
I feel Republic is very much still doable though, Phase 1 Clones can be built all-HIPS plastic using the Phase 1 helmets in the "Republic Specialists Personnel" set mounted on Phase 2 bodies. So long as you also wanted some Phase 2 troopers in your collection of course otherwise it's a more expensive addition.
As well as the Republic the Shadow Collective is another all-HIPS option, currently a more limited selection of models to choose from but going forward it is extremely unlikely they'd get any soft plastic additions to their range.
Hope any of this is useful, the hard plastics are leagues above the soft in terms of detail and crispness. Aside from the generally less ornate (or "Bling") designs of Star Wars versus Warhammer
40k I'd call them comparable in terms of casting quality and ease of clean up, mould lines in particular being very consistently shallow and easy to remove.
Cheers
Chris