Can we introduce something like toKisShared() for this? Writing a full shared poihnter name every time might be too boring at the global scale. We already have toQShared() for things like that.

I was always wondering, if there was any solution not to write the full name every time in such returns? The only guess is to return nullptr instead of 0 or full class name and make an implicit costructor for nullptr...

E.g. here nullptr would sound much more obvious syntax, I guess.

I don't find it so very hard, to write the constructor... but I also wonder if using a shared pointer is really justified in all cases. If you have a function that does some processing on an object, without holding on to it, then there is no need for any shared pointers, the caller can simply guarantee that the pointer stays alive for the duration of the function call.
If you really want, adding convenience API is of course possible.

I guess not easily. At least I can't think of a simple way, I can try to ask around.

It could of course be return KisPaintDeviceSP(nullptr);
but I assume that doesn't feel right to you either then...