I think you can do it all right for all MTLTextures you create. From what I understand, this is hint that lets Metal/GPU optimize texture to the usage that you plan for it, on the particular device. For example (now I am turning to guessing!) if your texture usage is just MTLTextureUsageRenderTarget maybe it could be stored in plain (not "tiled/swizzled" for texture unit caching needs) format, texel after texel, just like ordinary bitmap.
With that being said, as of today one does not have fine control over MTLTextures created by CAMetalLayer (so also MTKView) as drawables. However, if you look into header (and I recommend reading the headers in case of doubts with Metal, they often help):
/ This property controls whether or not the returned drawables'
* MTLTextures may only be used for framebuffer attachments (YES) or
* whether they may also be used for texture sampling and pixel
* read/write operations (NO). A value of YES allows CAMetalLayer to
* allocate the MTLTexture objects in ways that are optimized for display
* purposes that makes them unsuitable for sampling. The recommended
* value for most applications is YES. */
@property BOOL framebufferOnly;
So I guess setting framebufferOnly to NO should force usage of MTLTextures being returned as drawables from CAMetalLayer/MTKView to include more options (they specifically name sampling, read and write operations). Hope that helps.