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).