True. I hadn't considered that use case. Typically you want to off-screen render in MSAA and downsample blit to the system FB.
This came up at one point because drivers often have a way to let users force multisampling on applications. And this usually manifests as forcing multisampling on the back buffer, thus breaking the blit from the internal FBO to the back buffer.
Ah! Good point!
Does GL_RGB32I support for 4x or 8x multisampled textures in call glTeximage2DMultisample? Are there any other formats which do not support 4x or 8x ?