You know, background count as purely a modifier to limits might work really well... It would mean you have to pull more mana into you (higher Force, risking higher Drain) to accomplish the same tasks. It would still weaken spirit summoning, and wouldn't completely screw sustaining foci. Dual-natured entities would receive it as a limit penalty to all actions (minimum Limit being 1). Adepts would experience the lower limit on anything that's modified by one of their powers, or maybe only affect inherent limits (no BC making your gun less accurate because you're less magic than usual).
It would also make it more cohesive, as "good" BC already modified limits.
Although, it would mean higher BC is potentially even more crippling. Lowering limits by 1 or 2 is manageable, but when you get to 4 or higher, that could become a serious problem. It'd need playtesting...
The more I think about it, the more I feel like that would be the best solution.
It would give more value to reagents, which I like, and allow BC to be more ever-present without feeling as much like a penalty (as a reduced limit doesn't feel quite the same as a dice pool penalty).
I know I've heard people claim "We can't rewrite entire rules!" but that's simply not true; the MMRI echo in Data Trails completely overwrites the Mind-Over-Machine echo in the core book. And Rigger 5.0 introduced a new, fleshed-out set of rules for chase combat (labelled as "Optional"). If this would make the game more balanced and make people feel like they can actually make use of Background Count without feeling bad, then it's what's necessary.
So why not go back to the edition mentioned earlier then? That is have background count as a modifier to limits but reduce the amount of background count to values that were apparently in 4th ed e.g. most areas having a 0-1 count and the occasional spike to 3-4 and rarely a 5+ Background cout. That way 90% of the time a mage's actions aren't being punished as my walking around town and spellcasting is getting a 0 count as its the normal level, if I'm dealing with an area that has weird or prolonged suffering its higher and the big bad sections are a 5. Since its applied to limits that would be I think suitably challenging without utterly crushing a mage as written.
Some examples would be . . .
Rating 0-1Normal levels or significant but brief emotional or small but continuous spiritual or magical influence e.g. a violent crime, a small town church.
Rating 2Significant but brief emotional experiences shared by a LARGE group of people (>50,000?, >5,000?, >5,000,000?) or steady emotional or magical impact over several years. Examples include riots, cities with heavy pollution or a desnse population living in misery.
Rating 3Significant events over a prolonged period or time generating emotional significance over decades or centuries. Most of the great mana lines and power sites fit this category e.g. Gobekli Tepi nexis, Nazi Death Camps or the Chicago Zone.
Rating: 4Places that host significant events over a prolonged period of time where the events are still occuring e.g. stonehenge, arlington cemetary.
Rating 5The most powerful mana lines or events that have emotional or magical significance to most of humanity e.g. the great cain line in Tir Na nog.
Rating 6+
A background count of 6 or higher is considered a mana warp where the mana flows and surges chaotically. These are usually found in the upper atmosphere but there are other odd places that warped astral space beleived to be created by a combination of immense emotional impact combined with a m asive maniuplation of mana e.g. the aurora borealis.
Obviously needs more work but I think that would work better as well.