There are numerous workarounds they could implement, and I'm sure the think-tank type guys at Blizzard have numerous options on the table, if they wanted to offer a multiboxing friendly environment.

However, 90% of your customer demographic seems to be heavily against boxing, even if they're uninformed and don't know the differences between boxing and botting.
Catering to your 90%, to keep them as happy as possible, is going to be a better financial decision than catering to the fewer boxers, even if per person they bring in far greater revenue (lets say, for argument 10% of the demographic brings in 15% of the revenue).

The change was aimed at boxers, at least partially.
Otherwise the Arena change to Follow would not have been included.
Bots are not an issue in Arena, yet Follow was removed there too.

While the timing of the sale, to just prior to the implementation of the Follow nerf, is not necessarily related... Blizzard is not stupid.
They had to realize the removal of Follow, would essentially kill PvP boxing aside from world PvP.
With an overall declining subscription base, and boxers consistently picking up 5-10 extra accounts here or there... for RAFing 2-3 new teams, or to attempt 10/15/20 boxing... Boxers make up a disproportionate amount of the sales.
There is no way, Blizzard as a company did not know the Follow change was coming; it is not like, 3 hours before the patch some guy says, 'What if we remove Follow from BGs/RBGs/Arena'? with his supervisor saying, 'Sure, that's throw that in as an extra change'.

So the whole... big sale, which boxers traditionally take massive advantage of... combined with, they know Follow nerfs which will kill the ability to box for numerous players, are coming... combined with no warning of the change, in patch notes or on the Test Realm... combined with it also applies to Arena, where bots are not present but boxers are...
It is basically impossible for an intelligent person to not conclude: Blizzard is against boxing in PvP, because it negatively impacts their large percentage of the player base... but Blizzard still wants boxers to dump money into the game, for PvE... so is not outright banning it.