Well, for one thing, I don’t think it’s even worth wondering if we’ll get new Toa. Even if G2 goes on for more than three years, next year is (presumably) the big battle with Makuta and the MoUP, and as @Chronicler said, it would be ridiculous for LEGO to harp on the six Toa being those who will defeat Makuta and then replace them with a new team as the final battle begins.
As for sets, I don’t know what to expect, but I hope the Toa will be more unique, more in the vein of 2015 than this year. I like the Uniters, but they are too similar in construction, which reminds me of the latter years of G1, where Toa Teams tended to be relatively similar in build (now, the Uniters make up for that by having functions and ingenuity, but they’re still a little cookie-cutter for my liking). 2015 had builds that really highlighted the strengths of CCBS by creating uniquely-shaped characters with distinct physical personalities, and I’m hoping that 2017 returns to that philosophy. In terms of function, I’m not sure what else the LEGO team can come up with in terms of team-based functions. Arms and waist are really the only good “playable” functions for action figures.
Story-wise, I definitely want a more intense, stakes-driven story. Makuta should be a big bad worthy of the name, and the Toa should be pushed to their limits to defeat him, perhaps even getting defeated themselves for a time. Ekimu dying might be a good shocker, but it’s also something many might expect. Killing one or more of the Toa would be shocking, but difficult given their main-character status.
I like @ColdGoldLazarus’s idea about a Rahkshi-inspired wave of villains, but I’d be more interested in a group of “anti-Toa,” as that allows the people who want more Toa characters to be satisfied, and opens the door for more elements and cool masks. Titan Ekimu and Makuta sets would also be a nice thing to have–and, of course, the MoUP in set form (almost certain to happen) and the new Vahi (possible).
All in all, since this is presumably the finale and possibly the last year of G2, I hope LEGO will go all-out with sets and story, to give this generation of BIONICLE the final hurrah that G1 deserved. Hopefully, JtO will be renewed/extended, possibly with more episodes, and we’ll get a bunch of awesome sets and a great story to round out the line.
Although, if I had one wish overall, it would be that BIONICLE does well and merits a fourth, or even a fifth year.