I guess that's a reasonable position to take. It reminds me of paper publications where you have all the figures on color plates bound in the middle/end, so I guess it isn't without precedent
On the other hand, it made me think of old Usenet posts and discussions. That was another medium where you were limited to plain-text only. Posts were often forced to resort to awful ASCII-art drawings of things they wanted to explain and that was just a horrible experience altogether (not to mention how fun those drawings are to decipher today where modern archives have mostly messed up the white space).
Binary attachments were somewhat fiddly in Usenet, AIUI? I don't think MIME/8-bit clean support was really consistently there at the time. In Gemini, you'd just serve it as a binary file.
On the other hand, it made me think of old Usenet posts and discussions. That was another medium where you were limited to plain-text only. Posts were often forced to resort to awful ASCII-art drawings of things they wanted to explain and that was just a horrible experience altogether (not to mention how fun those drawings are to decipher today where modern archives have mostly messed up the white space).