Crafting Spell Gems (Out of the Abyss Magic Items)

So, I am running a game with a bunch of 3rd level characters, and one of the players has read Out of the Abyss... my favourite Campaign from WotC...
Point is, he thought any Spellcaster could just cast spells into regular gemstones to create Spell Gems...

I corrected this, by pointing out the specific rules in the 2024 DMG, and for now, there's no issue...

But it got me thinking: should I treat these as Scrolls, since they are functionally pretty much the same? And regardless, how would you run your players crafting magic items? I am tempted to require new (Homebrewed) Feats, but I don't want things to be overly complicated.

So, let's chat about it, please. Inquiring minds want to know!

Is this a similar case to a Hag Eye? (Crafting a Hag Eye)

- Creating a Hag Eye. Only a hag coven can craft this item, which is made from a real eye coated in varnish and often fitted to a pendant or another wearable item.

- Spell Gem: [...] Deep gnomes created these magic gemstones and keep the creation process a secret.

In any case, I'm following the 5.5e DMG rules for crafting, so the exceptions are common Potion of Healing and Spell Scrolls:

Crafting Magic Items

The Player’s Handbook contains rules on brewing Potions of Healing and scribing Spell Scrolls. To create other magic items, follow the rules below. In these rules, “you” refers to the character crafting the magic item.

EDIT: for clarity.