All it takes is someone (or group) interested enough to expend the resources necessary to re-implement it. But browsers are not going to support binary extensions. So an implementation might be in WebAssembly / JavaScript -- but then Flash becomes just a translation or transpile layer onto existing web technology.
If nobody implements an open source Flash, that is the proof that it is not sufficiently interesting to anyone with resources to build it.
All it takes is someone (or group) interested enough to expend the resources necessary to re-implement it. But browsers are not going to support binary extensions. So an implementation might be in WebAssembly / JavaScript -- but then Flash becomes just a translation or transpile layer onto existing web technology.
If nobody implements an open source Flash, that is the proof that it is not sufficiently interesting to anyone with resources to build it.