Closing it as it's actually already supported via 

exif_read_data('data://image/jpeg;base64,'.base64_encode(file_get_contents('image.
jpg')))

while the posted example will work, it requires a lot memory on php-side because you need to read the whole file + you need additional space for the base64 encoded string.

so its far away from an efficient solution and will not work for big/huge images.

After reading the comment of maggus dot staab at googlemail dot com, I reopen the ticket

It seems like all the exif_* functions do not support streams, I'm gonna take a look at it

I'm currently working on a patch, and a side thing that is coming out of this is an additional $context parameter for use with non streams, since internally PHP is creating a stream with no context, this can help work around supplying direct addresses like locations thats gated by custom protocols or HTTPS which would need peer verification or similar.

I expect this patch to only go in PHP 7.2 and onwards.

I have just implemented this in master, it will be available as of PHP 7.2.0 Beta 1!

Thanks for helping PHP become EVEN greater!

ps, it also works for exif_thumbnail()