Until relatively recently, STM8 devices did not have a usable GDB debugger, so VisualGDB could not be used with them. Currently, it looks like there is an unofficial port of gdb and binutils (although you still need to rely on SDCC instead ofGCC), so you might be theoretically able to get it to work by following this tutorial. That said, we have not investigated this at all and cannot promise that it will work. We will try to do a quick research into STM8 around Q3 2019 and see if the available tools are sufficient to provide reasonable building/debugging experience.
Alternatively if you can confirm that the underlying tools are fully usable (and share details), we should be able to update VisualGDB to support STM8 out-of-the-box earlier.
It’s not exactly a secret, but we constantly update planned feature priorities based on the feedback we get from users, new releases of popular frameworks (and changes of framework popularity) and so on. E.g. we were originally planning to postpone the advanced mbed project subsystem to v5.5, however as the mbed popularity kept on rising, we decided to push it into v5.4. Hence the best way to learn about the latest VisualGDB features would be to follow us on Twitter and watch for the announcements of preview builds and new features.
Sorry, it is still in the queue. ST recently released a few other device families (STM32MP1 and STM32WB) that got prioritized over STM8. We will likely get a better estimate for STM8 in the next 2-3 months.