Limiting attribute augmentation is not the ideal way of balancing magic. All character types/archetypes should have access to multiple augmentations without having to resort to sacrificing their archetype (magic, resonance, ect.).
At first, I was like "Yeah, makes sense".
But then I asked myself: "Why exactly?"
Why do mages
have to be able to boost multiple Attributes with "their" Attribute enhancement perk? Isn´t that mentality devaluating Augmentations and Adept Powers? And on the flip side, can Adepts and mundane characters summon spirits or cast spells? Can mundane Characters Astrally percieve? And do technomancers have
any perks at all that offer any kind of attribute enhancements?
Right now, despite having a ton of other powerfull tools at their fingertips, mages just needs just one(!) spell and some ranks in Focused Concentration (or alternatively, sustaining foci) and they are able to buff up multiple Attributes during their morning breakfast routine, for a total sum that Adepts and Augmented can only dream of. Furthermore, the enhancements from
Increase Attribute can affect Attributes that are off limits for Samurai and Adept perks, they can be adjusted for different Attributes when needed
and they can be bestowed to other characters.
Restricting
Increase Attribute to one appliance per target would be (or rather:
would have been?) just the right measure to
- Balance out the increased flexibility of the Spell in an organic way
- Give Adepts and Augmented mundanes a niche in which they can outshine pure mages (at least to a degree, that new flexibility of Increase Attribute is still a banger)
- Make drain an actual thing that matters. Frankly, I´m suprised that so many people here don´t even dare to question the fact that mages can easily head for +8 Drain dice right out of chargen anymore

- Promote more teamplay, since you retain more value from the spell when using it to buff up multiple characters and not just yourself.
Even with that nerf,
Increase Attribute would still be safe pick in most spellbooks. And if you still insist that mages
absolutely need multiple Attribute enhancements in their toolkit: That´s not even gone with that change. There´s still MysAds, the option to sacrifice 1-2 points of magice for lightweight augmentations, Combat drugs and the separate
Increase Reflexes spell.
TL;DR: Increase Attributes should be restricted to one appliance per target, and there´s ample reasons to do so.