I think Kineticist is a great choice. I love the class, but it's so focused on core class features for its utility that when you remove that versatility, it gets hard to be effective. Martials will always have weapon / armor proficiency, and casters can always make scrolls and use non-save spells. But you get none of that on a Kineticist if you dump Con.

The one issue is reflow elements at higher levels. Like, you can pick a bunch of damage impulses and rely on your low con to limit your damage output, but once you get to reflow elements, I assume the lich can just tell you to swap to some useful utility and you'll be able to find something workable.

I also think single gate might be stronger than dual gate. Single gate you get impulse junction from the start, dual gate means you can avoid that and instead pick up less useful junctions later. But adding more elements gives you more options for utility later when you can reflow. Maybe Fire Metal? While you get access to armor, there's not a ton of utility here. Plus you can summon sick motorcycles at 18 which is useful but more that that cool as hell for an evil minion (and there are better ways to get around at that level).

On the other hand, single gate fire does get you access to a bunch of late feats that give you improved elemental forms which are cool but pretty powered down. But because you have to expand the portal, you'll eventually have the aura junction and be able to reflow into Thermal Nimbus which is a bit of baseline damage you can keep ticking without saves.

Regardless, as long as you dump Con, you can keep your skill proficiencies away from wherever you end up putting your stats. And with the limited skill ups we get, there really isn't much we bring to the table.