Who is your target customer?

Someone who runs a website that needs a chatbot, to try and find an off the shelf chatbot?

Seems a tricky value prop. Most websites don't need or want chatbots. Those that do, how many want off the shelf but not free chatbots?

the initial target customers would be devs - this would be a chatbot hosting service of sorts.

However the idea would be to later expand to a store (like the App Store or Play Store but for bots - devs get paid, people get bots, my service is the middle platform)

Devs are notoriously cheap. Tricky market to crack. Just having an app store I don't think would be enough to get much traction.

It depends on what you mean by a "chatbot platform".

If it's a way of developing a single "chatbot" and having it work across multiple "platforms" (think slack, hipchat, irc, facebook, standalone, etc... maybe even including voice-specific platforms like Amazon echo and Google Home). I would LOVE that. However it's going to most likely suffer from the same issues as other "platform-independent systems" which is that you'll be developing to the lowest common denominator.

If it's just a way to make a chatbot via a GUI, I'm personally not interested at all.

The way we handle this (and avoid the lowest common denominator problem) is allowing you to have one bot, but then specific 'modules' that execute only if being accessed over a specific network.

This lets you build one bot that supports everything from SMS to Messenger to Slack in the same interface.

Other tools I've seen apparently do automatic conversion of one rich media form to another, but I'm less keen on that idea personally.

The idea is just as you mentioned - a platform where you'd basically create a bot (by that i mean, your code will be given a context, and your response would be forwarded to the chatting service - be it slack, irc, etc.)

Furthermore, with an base SDK, you'd not build for a specific service, you'd build it for MY service and it'd handle every other service out there (insert XKCD joke about different platforms here)

Also as for GUI, it's not a requirement - it's for those who are not programmers but want to a chatbot for their Echo or Home etc. (an IFTTT of sorts if you will).

Also it'd have extra stuff that devs won't have to worry about (like hosting or charging users, promoting etc.) - all of which would be handled by my platform).

Checkout AI .API. This sounds like!E what you might be looking for.

Isn't there a lot of competition in this space? It seems like your bots would need to be particularly intelligent or the interface would need to be particularly low friction.