Special attackers
Assuming gym rework introduces species limitation (for example only one of each species in the same gym). Do you think specialists (attackers) will have no use?
I mean there is no point to bring jolteon into the battle for only one gyarados (comparing currently there might be 4 or even more garys). And same applies to whichever ice attacker you are using (lapras, cloyster, jynx...). Will these attackers be useless? Or at least their value will drop? Of course if prestiging will still exist these mons can used to prestige but I am talking about attacking.
Answers
The question assumes there still will be a fixed order of Pokemon in a gym, that there will still be a numerical limit to the number of mon allowed on an attacking team, that you will still be able to see the lineup of defenders before attacking, that gyms can still be taken down, etc. Until we know what the rework looks like and how radically different it will or will not be, I don't see a rational way to address this question.