Depends on what you do... and we can't predict that.
I run up to 12S 5000 mah now, with plans to go to 18S 5000 mah. But I buy 3S and 4S packs for better cooling. A 6S pack tends to have the center 2 cells fail early.
More important than being able to charge high cell counts is being able to charge your packs at a good rate. A typical 50 watt LiPo charger can't charge a 4S pack at much above 3 amps. So even if you stick with 4S as your biggest pack you may need to look at higher power chargers.
Then there is the ability to charge packs in series and parallel. Commonsenserc.com sells an adapter for series charging a pair of 3S as if they were a 6S and there are "balance boards" for charging several packs in parallel. In combination with a high power charger you can get lots of packs charged all at once instead of spending half a day monitoring the charger for preparing to head off to the field.
Many things to consider when looking at new chargers...