Considering the modularity of the platform, I'm a little disappointed that the aftermarket hasn't taken more advantage of it. A lot of the mods out there are superficial, cosmetic, and external. Almost no one makes internal parts for them, except for maybe the actual trigger. Where are the tool steel sears, for example? How about an entirely CNC'd FCU built for precision fitment (e.g. for one, flat FCU slide rails for perfect slide fit)? How about a custom FCU + grip module designed to take Glock mags, if only to troll the internet.
There probably couldn't be a better platform to enable this.
On the subject of safety, there are probably a number of modifications that could be done. Maybe double the height of the sear face. Also, double the width of the striker foot that engages the sear face. Overall creating a broader contact patch on the sear with more travel. Then, increase the length of trigger travel. I'd love to see the dual, little, sear springs replaced with a single and more substantial spring.
Also, I'd love to see a redesigned sear and trigger bar that physically prevents movement of the sear unless the trigger is pulled. Theoretically, in current form, inertia can still move the sear. This is true of many other striker-fired guns, such as the VP9. Whether it's an actual issue is debatable. Regardless, I'd like the peace of mind of a sear that can't physically move, similar in concept to Glock's drop safety ledge.
Also, redesign the striker housing and FPS so that the FPS is no longer a lever arm and is a more conventional block or cylinder that articulates linearly. How about a striker housing + striker with much tighter fitment since the stock unit feels a bit sloppy. Also a redesigned striker housing to eliminate that little striker return spring. Maybe none of this would do much of anything, but I think it would at least be interesting to see the aftermarket experiment with it. It's the possibilities like this that make me almost want to buy one of these again.