Combining via filename is the fastest way to do it. If you happen to have multiple images with the same filename on a contact sheet (for example if you have multiple individual folders combined into a single contact sheet), the images that are in the same folder will get combined. So I do need to point out that the RAW and JPEG that you are expecting should be joined in the screenshot you posted (the images of the kids at computers) have different base filenames:
The JPEG is: _MG_0088_C.JPG
The RAW is: _MG_0088_C_2.CR2
So even if we did what you are suggesting, the files you are wanting to be combined would not be, because they fail the first and fastest check of sharing a base filename.
However the metadata is there and Pm could distinguish between 2 very different images and not combine them. 'Content +size+creation date+Camera+HASH' can be used to decide if they are combined or not.
Regarding size and hash: Neither of these would be the same between a RAW and a JPEG.
By "content", do you mean the actual content depicted by the image, or do you mean metadata?
Naturally, we do already get the camera model and the date (although I assume you really want the capture time, as the file creation date for a JPEG might be much more recent than that of the RAW file if you're editing in Photoshop and saving out a JPEG), so this could be used for joining the files on the contact sheet, although if the metadata is not yet gathered for all the images on the contact sheet, this will not be as instantaneous as it is when joining strictly by file name (and on slow drives like NAS's this will be very slow, similar to how sorting by capture time is slower than sorting by filename)
So, we can consider your suggestions, but it's not going to solve your problem today (and if we do implement it, it wouldn't be for a while). What can solve the problem today is a good naming scheme, as Alex suggested. You could even take the date and camera model variables and rename your images with them and Photo Mechanic will end up doing exactly what you are asking.
