I got my first Delica (in AUS-8) 20 years ago. I still love the Delica, own several of them, and IMO the D4 FFG is the best version of it yet. Personally, I like it in the VG-10 steel over the more 'super-steel' versions. For me, it has the right degree of edge-taking and holding, ease of resharpening, good corrosion resistance, etc. In fact, it's ridiculously easy to touch up/resharpen.
Could there be improvements? Of course. Although it's pretty pocket-friendly to clip on, IMO there could still be a bit more smoothness where the clip contacts material. And I have heard that the clips are soft and can sometimes snap off if snagged. So maybe tougher, more durable clips, and a surface area on the FRN that's even smoother where the clip contacts, but where the clip can still press against strongly enough for retention. The clip on my Native 5 LWT feels tougher/more durable, but the FRN surface it contacts against tears up my pockets, so I can only carry that one down in pocket unclipped.
If someone asks to suggest an EDC knife (single blade), I usually suggest the Delica first. Especially if they are aware a knife is for cutting and not prying, I will suggest the FFG.
Jim