The problem of Elemental Magic came up in the errata thread. There are definitely issues with it, one of which is that parts are unclear (the XP bonus), and one of which is that it seems to be rather weak for a Major Virtue.
For reference, here is the full text:
You have been trained in the ability to manipulate raw elemental forms (Ignem, Auram, Terram and Aquam), and view them as a connected whole rather than four separate Arts. Whenever you successfully study one of these Arts (that is, gain at least one experience point from study), you gain an additional expe- rience point in each of the other three.
Your elemental magics are also more flex- ible than those of other magi — there is no dis- advantage in adding elemental Form requisites to any elemental spell. If an Aquam, Auram, Ignem, or Terram spell has another element as a requisite, you may ignore the requisite. You must still use the primary Art, even if the req- uisite is higher.
I am currently planning to add the current erratum to the first paragraph:
If you gain experience in more than one Form in a single season (perhaps from Adventure experience), you gain a total of one free experience point in each Form, no matter how many Forms receive experience from the season.
What else needs to be done? The first sentence of the second paragraph could be deleted, which would make the intent clear, I think. (The description of the misunderstandings suggests that they rely on that.)
Possibilities that occur to me:
Knock it down to a Minor Virtue. It isn't used by many example magi (just one of the core rule sample characters), so this is not a difficult change.
Boost the number of bonus XP you get. For example, "When you study one element, you get half as many XP in each of the other three elements. If you get XP in multiple elements, you get bonus XP in each element based on the highest applicable gain, not counting the bonus XP, just stop that powergaming right now." This is a lot more powerful, but it might still be OK for a Major Virtue. I bet it would make elementalists take the Virtue… You could also hand out half the gained XP to be distributed between the other three elements, but this is probably not quite powerful enough by itself.
Do something with Similar Spells, so that all elements are similar to each other for the magus.
Allow them to change the element of spells on the fly. This is a lot of work for new players and troupes, but might be the most interesting option.
I'm open to other suggestions, and comments on what is over- or underpowered in my suggestions. Basically, as a Major Virtue, it should be the obvious pick if you want to play an Elementalist, unless your variety of Elementalist is clearly best captured by a Major Magical Focus.