My take on what their kid would look like, thaumaturgically:
Magic Circuits
It's noted that Rin has a quite high number of circuits (forty), and Shirou also has an above-average amount (twenty-seven). Rin has above-average quality of circuits, and Shirou has low-quality circuits (although that may not be his natural state, considering his building circuits from nerves and all).
As these two factors seem to be at least somewhat inheritable, then the child would probably have a significant number of magic circuits of at least average quality.
Origin & Element
Element does seem to be at least somewhat inheritable; for example, the Makiri/Matou family has a pretty consistent Element of water. But it's not completely predictable; Rin and Sakura both have very unusual elements (All classical elements and Imaginary), and I quite doubt that either of their parents had either.
Shirou's element at biological birth is unknown, and his element of 'Sword' is certainly from his later more artificial birth - which would hypothetically have an inheritable impact is unknown.
If you must have a more unusual element for their child, then go with Metal, but I would consider one of the classical elements to be most likely (Fire or Earth, perhaps).
Origin is most definitely not inheritable; your origin is your fate, your destiny (or more the other way around; your origin attracts what you would consider your destiny). Shirou's was changed by Avalon, but I would argue that that's more the result of him being for all thaumaturgical intents and purposes a breathing corpse when it was implanted.
Magic Crest
Now this is where it gets interesting. I don't know if someone can inherit circuits passed down from both parents, but I don't see why not. Does this mean that Shirou could 'contribute' to the Tohsaka crest (or start a new Emiya crest)? Perhaps. And certainly then at least some of his abilities might be thus inherited.
Actually, considering the sorrow of Sakura and Rin, I would consider it quite likely that one kid would inherit the Tohsaka crest, but Shirou would donate some of his to the other kid as a first-generation crest (ie, creating effectively a cadet branch of the Tohsaka family). And maybe Rin would donate a couple of her circuits to such an endeavor.
Hmmm... I know that the crest is formed by each heir donating a circuit or two when it comes time to pass it down, but is there a limit to how much can be donated?
Heh... more fun would be in a situation that includes Saber; she has a Magic Core, rather than circuits.
Magic Circuits
It's noted that Rin has a quite high number of circuits (forty), and Shirou also has an above-average amount (twenty-seven). Rin has above-average quality of circuits, and Shirou has low-quality circuits (although that may not be his natural state, considering his building circuits from nerves and all).
As these two factors seem to be at least somewhat inheritable, then the child would probably have a significant number of magic circuits of at least average quality.
Origin & Element
Element does seem to be at least somewhat inheritable; for example, the Makiri/Matou family has a pretty consistent Element of water. But it's not completely predictable; Rin and Sakura both have very unusual elements (All classical elements and Imaginary), and I quite doubt that either of their parents had either.
Shirou's element at biological birth is unknown, and his element of 'Sword' is certainly from his later more artificial birth - which would hypothetically have an inheritable impact is unknown.
If you must have a more unusual element for their child, then go with Metal, but I would consider one of the classical elements to be most likely (Fire or Earth, perhaps).
Origin is most definitely not inheritable; your origin is your fate, your destiny (or more the other way around; your origin attracts what you would consider your destiny). Shirou's was changed by Avalon, but I would argue that that's more the result of him being for all thaumaturgical intents and purposes a breathing corpse when it was implanted.
Magic Crest
Now this is where it gets interesting. I don't know if someone can inherit circuits passed down from both parents, but I don't see why not. Does this mean that Shirou could 'contribute' to the Tohsaka crest (or start a new Emiya crest)? Perhaps. And certainly then at least some of his abilities might be thus inherited.
Actually, considering the sorrow of Sakura and Rin, I would consider it quite likely that one kid would inherit the Tohsaka crest, but Shirou would donate some of his to the other kid as a first-generation crest (ie, creating effectively a cadet branch of the Tohsaka family). And maybe Rin would donate a couple of her circuits to such an endeavor.
Hmmm... I know that the crest is formed by each heir donating a circuit or two when it comes time to pass it down, but is there a limit to how much can be donated?
Heh... more fun would be in a situation that includes Saber; she has a Magic Core, rather than circuits.