You have enough incentive enough for raiding in one platform or the other based on player preference. A change like this which penalizes a platform further is nothing more than you picking favorites and it WILL cost you subscriptions.
Who is being penalized? Fun Fact: "Penalized" implies you are serving the negative consequences of your actions. If you want to get technical, one could easily claim 25mans are needlessly penalizing themselves for choosing 25man raiding because they offer very little reward for the sheer quantity of effort that goes with the choice.
So who is really being penalized?
A successful company will find ways to keep new customers as well as older customers. If we took at 25man raiding through this "business POV" why are 25man "losing costumers" to 10man raiding? As this thread has pointed out, the logistics are tough. In addition to just being harder to get the ball rolling, 10man raids offer the same rewards. How can 25man attract players away from 10man, for both newer and older players? Gear helps, but that's not the solution (which we've also stressed for ~38 pages, at the time of this post)
25man groups are simply harder to setup. They require the same amount of personal responsibly from player to player, regardless of what 10man raids claim. (Trying coordinating 24 other players, making all player work together in sync to achieve progression -- 10man is a joke when it comes to logistics). There is literally no incentive to keep 25man raids going, beyond the sheer will of the 25man raiding community. Who cares about gear when you're done with the tier? Aside from going full BiS (which is more of a preference than an actual incentive), very few players are thinking purely about Gear. It's all about getting the progression kill, the gear will eventually come with the progression and farm (Having the best gear available is different than having the best gear currently available to you).
Food for thought:
There are two options. 25man raiding and 10man raiding. 25man raiding is dying, no denying that. Logistics are the primary cause for this decline in 25man groups. 10man is thriving. 10man has always thrived. Giving 10man the same rewards as 25man raiding has contributed to the decline of 25man raiding. Offering more loot in 25man raiding did not help 25man raiding. 10man continued to thrive on the deaths of 25man raiding. Wouldn't it be "picking favorites," in favor of 10man, if Blizzard decided to let 25man die out?
Go into LFR. Consider the real mechanics of Heroic/Normal modes. Apply that to Heroic/Normal 25man raiding. Now bring 1-5 idiots to your raid. Three (3) of your better players leave. Add 3 more inexperienced players. Now there are 4-8 idiots/inexperienced players in your raid. Welcome to the death of 25man raiding in a game where you're rewarded for choosing the easier path. Again, logistics are the issue. Reward the players for the logistical challenge.
Just to restate what has already been stated in this thread:
- Better RNG on RNG gear (with RNG stats?) is not a good incentive.
- 25man needs a "Wow!" factor to which 10man simply does not have access. It will be overkill when both 25man and 10man agree that the idea is "too good," but it will be necessary.