I don't agree that feet are THE focal point of the tickling fetish. A flag or calling/cute business card is more like it. I think the true focal point of the tickling fetish is the healthy physical and mental thrills of it as well as playing with the exchange of power. I'm certainly not saying that feet aren't a popular element while also being a commonly sensitive area, but it really comes down to it being a socially acceptable way to see tickling, in my opinion. Media or literature or non fetishists want to play in that respect and what do they do? Go for the feet. They're on the opposite end of a lot of their defenses and if you have at least one person to keep them restrained then they're screwed and it's heelarious. They're often exposed already, easily exposed, not typically seen as a sexual region and you don't need to awkwardly undress anything (especially getting near a woman's breasts and be mistaken for using tickling as a ruse). It can be done easily in innocent fashion so it's been displayed that way forever. Doesn't really have much to do with what is the most sensitive area because that is so unique from person to person. One person could be their scalp, the other their neck, another their underarms and one could be the feet but ONLY if you do it a certain way (really lightly, etc).
Now to the other side of interest in feet from a fetish angle: yes, a foot fetish and a tickling fetish can easily compliment each other. Those interests from my experience developed at the same time as I awakened sexually. We can argue all day about where they originate and why they are, but I think the question is more in respect to our individual perspectives and motivations. The tickling is about power exchange. My interest in women's feet is like an artistic thing. I see them as a symbolic, physical ambassador for womankind. Feminine, graceful and architecturally devine (depending on hygiene and even "non radiant" feet are still more attractive than men's, of course 😉) . The visual cue of them turns me on and it isn't as simple as, "OMG FEET BONER HUH UH". It's easy to reduce it to that, but it is the woman/women I'm enamored with. That's the root of it and I wouldn't want a woman spending time with me to think that they're separate from what's going on in my mind. The arousal skyrockets when it is somebody I really like (perhaps regardless of how either of us would physically rank them). It's more important that they belong to HER. It's a mistake to think that "well, any feet in a storm, I guess". That's a bit too cynical. And it certainly isn't the be all/end all. It definitely doesn't mean I find other parts LESS interesting. That's unfair too. Most of us with a large sexual love don't even have a technical fetish because we are capable of being turned on by other things and simple physical contact.
It's unfortunate that the general view of a foot fetishist is either a Ted Bundy type or the guy that gets arrested breaking into someone's home. It's not interesting to hear the story of well-balanced fetish guy so all women hear about the majority of the time is stuff like that or, God forbid, a mentally unbalanced individual approaching her. Judgement is passed without a lot of info or education because there's no interest to obtain it or they're unlikely to run into somebody with the positive end of it and talk it up. All that said, adventurous and open-mind peeps tend to understand where the fetishes are coming from and can at least respect it, even if they don't share it. And I think even though I love both feet and tickling, there's so much I love about tickling that I wouldn't have it be isolated to any one thing. My tastes run wide and varied. And I think many are in the same boat.
Anyway, that's my two. Or thirty.