I'm running a customized setting with different realms and different spell lists (although many are based closely on the SL lists). So, originally rather than constructing base lists, I just gave all magic-using professions free choice of 6 base lists. Personally, I do not recommend this. It really only takes one base list to get most of the combat functionality of a magician, and similarly for whatever other functions you want. You get a big power boost for your spellcasters while the real functional differences between them start to disappear. And by power, I mean both that they are more potent and also, more importantly, they step on a lot more toes overshadowing the roles of other party members.
Since then, I have narrowed it down so pure casters get a choice of 6 out of 10-12, and semis get a choice of 6 out of 8-9 (although in practice most semis only take 3-5). I'm happier and my players like it better too.
General feedback on the forum in the past has been that even opening things up that much is a bit much, and it would be better to have a couple specific packages that are treated as variants on the original profession. E.g. you might have a variant magician specialized in one element, who gets an existing Law list, the two most related elemental Law lists, a variant list on their main element (e.g. the Mastery lists from the Essence Companion), an elementals list, and something else. But it's a fixed thematic package, you get that or the original package, you don't pick and choose.