I suggest adding a new item property to gear of all types which can be used to denote what upgrades can be applied to it through existing and future crafting systems.

How this would work is as follows...

Shroud items could be assigned the item property "Attuned to Shavarath" this property would state that shroud items could only be altered in the three altars found in the shroud or any other alter stated to be "Attuned to Shavarath". IE, nothing besides shroud at this point, but open to others in the future.

The new crafting system already has a modifier "craftable" that can be renamed to show that it can be used with festival and ritual recipes.

Other named craftable gear of lesser quality then shroud for it's ML could have a modifier allowing rituals and festival recipes...

Basically the idea here is to create a unified set of modifiers on gear that is easy to read and apply rules to for various crafting mechanisms. We all know that gear is created far from equal and some gear could be offered more crafting options to make up for weaker basic design...including for example more powerful augment slot options for certain epic items. In that case the recipe itself would call for an item with the appropriate item property instead of tying it to the altar itself. This would be an interesting way of adding more varied 'upgrade' options on gear without the extremely limited options of it being on a single named item or very weak in nature to prevent undue power creep from it being applied to already strong items.

I think this would be an ideal way to add more 'upgrade' paths for items that was safer from a balance standpoint and a coding standpoint as well as being easily understood by users.