This healing change has nothing to do with "the stat squish". "The stat squish" is an imaginary problem that could be solved with decimals, number truncation or just proportionately nerfing everyone. The healing change is based on the perception that...actually, I'm not sure why this change is supposedly taking place. Because healing is too easy? If that's true (which I don't think it is), that's more a function of encounter design, not having "too much" mana.
First, play a Resto Shaman in a raid, especially a 10 man heroic raid (though any Firelands raid will suffice). Play it well. Play it borderline perfectly.
Second, play a Holy Paladin in a Firelands raid, any setting will suffice. Play it well. No need to play it borderline perfectly though.
Unless your powers of observation are completely nonexistent, you will notice a very huge disparity in the abilities of each healer, tied primarily to their mana bar. Both are limited in their AoE healing ability, so what really sets the two apart when it comes to overall effectiveness is their mana bar. You should notice that a fight where a Resto Shaman goes completely out of mana is a fight where a Holy Paladin sees the boss die with 50-60% left after having done very comparable amounts of healing. Their regeneration tools (Divine Plea and Judgement of Insight vs. Mana Tide Totem, Telluric Currents and Resurgence) are probably reasonably close in value in blue gear. As time passes, though, and both gain more maximum mana from intellect, a Paladin's mana regeneration will eventually far outweigh that of a Resto Shaman. Because Divine Plea is based on your maximum mana pool, while Resurgence and Mana Tide are based on Crit and Spirit respectively.
The answer is one of two things:
1 - Change Divine Plea (and all other max mana regeneration) to scale from spirit (or some other secondary stat) instead of total mana.
2 - Change Intellect to no longer increase your mana pool.
So what are the pros and cons of each?
1 - While this seems like the more obvious solution, it's also homogenization. Different healing specs should work differently. They are already probably a little too close in the 3-heal system. Normalizing mana regen is harder to do with non fixed mana pools than it would be with fixed mana pools. It also makes Divine Plea useles for Protection and Retribution and will require compensation there.
2 - While this seems like a silly solution considering Intellect has always increased max mana, and characters feel stronger when their max mana increases, it has a lot of positive side effects. One, it allows different healing specs to be different in how their mana regeneration works, but prevents one spec from completely out scaling the other. 2 - for an Arcane Mage for example, increasing intellect in a non static/secure way is problematic as the higher their mana is as a percentage of their maximum, the more benefit they gain from their mastery. When you gain a ton of max mana due to a proc, it just interacts strangely with it. Static intellect, however, is so extremely valuable for them that nothing else matters at all compared to it. Removing max mana increases from intellect solves this problem as well.
While seeing your mana bar increase as you gain intellect, and better gear, seems interesting, it's really just a number and nothing more. A number that causes a lot of problems and its only benefit is "that number is bigger than it was before, I feel stronger!"
When your Heal spell heals for 10,000 instead of 9,500, you'll still feel stronger even if your mana number isn't higher. Static mana not increasing really doesn't take away from that.