[[WMG: When Shirou gets back to the Nasuverse...]]
he's going to damn well try to make sure Rin never finds out about Rule of the Underworld's monetary powers.
* Unfortunately, he wrote it in his journal, which somehow made it back before him. I pity him for when he comes back...
** Then again, he's magic resistant to the point of nigh-immunity now. So maybe he'll survive.
** She doesn't need magic. She just needs to walk up to him and [[CheshireCatGrin smile.]] He'll beg for his life before she even says anything.
*** That is, assuming Ilya doesn't immediately tell her to stop doing weird things to her oniichan and get lost. The last I checked, Ilya wasn't someone Rin would want to go against.

[[WMG: The reason why the diary Shirou sent to Sakura had hastily-written note on it was ...]]
Shirou's godly harem.
To elaborate: by the time he finds a way to send it, his harem of divine ancestors, goddesses, fallen goddesses, and whatever other super-powered beings there are in Campioneverse, will have gotten more members, one or two of them quite insistent on him staying with them instead of returning. Because of them, he started carrying the diary with him all the time, and had to sneak out if he wanted to work on a way to return home.
Once he had found a way and it happened to be too small, he had to act quickly to send the diary before his harem caught up to him (or rather caught ''him'') and thus had to quickly write the note using Arondight.

Jossed as of chapter 32. Avoiding spoilers, the portal he found was just too small for Shirou himself and was collasping even as he scrawled out his note to Sakura. ... That's not to say his harem, current and future members alike, won't turn out to be resistant to his plans of going home though.

[[WMG: The next member of Shirou's harem will be the goddess Inari.]]
I don't know how exactly would that happen, but considering that the overall plot had already been derailed from the one in Campione it's not outside of the realm of possibility. Sure, she would be an original character but for as long as they are done well there's nothing wrong with that.
And considering that she is a Japanese goddess (and thus possibly a YamatoNadeshiko with LadyOfWar traits), and a patron of swordsmiths among other things, she could be a good match.