my impetus for this was less about saying that manifestos aren't real unless they have numbered points (which i do like cos they give GRAVITAS and faux seriousness but isn't actually important), and more as a jumping off point to express the idea that manifestos are most powerful when they become frames for seeing things differently and guides to creating new things.
in that sense the manifesto jam is totally a manifesto itself. it says hey, here's an underexplored way to do writing and thinking and sharing that isn't constrained by traditional structures OR traditional means of distribution.
Any definition of art is doomed to be incomplete and to be always playing catch up. Once any boundaries are erected anyone can just move past them. Likewise definitions of games in this way are also always limited (and definitions of manifestos... which is why I hasten to add this post script).
Instead what is useful is if you can create definitions that while flattening an object from one/certain dimensions also better afford it to grow into interesting shapes along other dimensions. But NEVER a definition that makes growing along "unwanted" dimensions verboten.