Well if you use today as a guideline, then they would have actually said: 4 Tuners? We’ll give you 4 guides for that today. But if you buy more tuners in the future, you’ll need to buy subs for them.
I think they certainly could have given a grace period for existing users. Let’s say for 1 year if you buy more hardware, they will comp you the extra guide sub to bump up your concurrent guides to work with their new software model.
And the funny thing is they would see a sales boost from existing users who want to lock in another guide with hardware they didn’t need to buy.