I'd probably limit it to a max number of seasons equal to either Artes Liberales, Philosophiae, or Magic Lore.
Not a bad idea, but I'd probably limit it by Magic Theory instead. That is after all the main ability used for creating enchanted items - the ones you listed are only used in some special cases.
But there is also a reason why I specified "consecutive seasons". Spread it out over too many seasons, and you can be sure there will be some interruption preventing work in one of them.
Magic Theory is one ability that Magi already invest in. The others are less so, so gives more of a limit to the number of seasons. Plus, if you do it by Philosophiae, it kinda mirrors the Elder Verditius Runes, except you can do it by Magic Theory per season, for a number of seasons equal to Philosophiae, while a verditius can use the same amount of Vis, in one Season.
It can always be a new ability which requires its own study...
Nop...
The season limit is Theory * 2.
With this discovery, opening the item in multiple seasons, the limit becomes (Theory * 2) * Seasons.
If Verditius with Elder Runes doesn't know how to open for multiple seasons, it will probably be surpassed by those who can.
Perhaps your notion came from the fact that verditius multiplied Theory by Philosophie (instead of * 2). It makes sense for them, but not for this new acquisition, as it would be even more inferior to verditius for spending more than one season.
unless you combined it with verditious. Being able to spend magic theory*philosophae pawns per season for (new ability) seasons could generate some really massive totals.