As a practical matter, my suggestion above could be implemented simply by expanding upon the "skill book training" system already in place. However, rather then simply improving chances of success as with the current training books, at higher rank some synths / results would simply not be possible without the appropriately trained "skill book".

This would allow for the majority of such skills to be metered out through the accrual of guildmarks within the appropriate crafting guild. SE already has in place a mechanism by which skill books are only achievable once a certain rank is acquired. A further extension of this requiring certain skill books to be already bought before a particular later one seems in the realm of the possible.

However, additional sources of skill books are also possible : quests, purchases from Grand Companies -- even rare drops could be added.

This would require an expansion of the crafting skill book UI. Whether that is possible ... I must defer to the experts at SE.